What is the MOST economical way to get a second key FOB that I can use to drive the vehile normally?

Does your fob have a black or silver logo on the back?
The instructions in the links below worked for me. I have a black logo fob (non-sks / Prius without the security system) and I bought a used FOB from ebay for about $99. Using this method It took me three tries, and then if finally worked.

Finally! How to program a non-SKS key/fob. Detailed! | PriusChat
How to Program a New Key Fob for Full SKS Functionality | PriusChat

From usnavystgc:

Action steps are BOLD

PROCEDURE A
This procedure (steps 1. through 5.) is to be used for both the black and chrome logo key fob. This will program the fob to Start/stop engine while it is inserted into the key port. All new fobs should be programmed for this regardless of logo or SKS functionality
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1. Insert old fob (your fob that currently works) into slot and remove it 4 times in a row, and insert it a fifth time but leave it in there!
2. Open and close driver door 6 times.
3. Remove old fob from slot. Car is in fob programming mode at this point. Red anti-theft light remains on.
4. Insert new fob and leave in the slot for a full minute. Watch the blinking red anti-theft light on the dashboard. When it stops flashing and goes dark, your new fob is all set.
5. Remove the new fob and you're done with the START/STOP portion of programming ( if you have SKS, proceed to PROCEDURE B don't have SKS, proceed to PROCEDURE C).

PROCEDURE B
This procedure (steps 1. through 10.) is for chrome logo key fobs and vehicles with SKS functionality

Lock/unlock doors remotely + SMART KEY functionality
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1. Open the driver door and leave it open with no fob in slot (ensure the driver door is unlocked). Other doors can be locked or unlocked, it doesn't matter.
Complete step 2 within 5 seconds
2. Insert old fob into slot and remove it twice.
Complete steps 3. and 4. within 40 seconds of completing step 2.

3. Close and open driver door twice.
4. Insert and remove old fob once.
Complete steps 5., 6., 7. and 8. within 40 seconds of completing step 4.
5. Close and open driver door twice again.
6. Insert old fob in slot and close door.
7. Without pressing the brake, press power button, wait a second, press it again, wait a second, press it a third time to turn car back off.
8. Remove old fob from slot. You'll be in "add mode" at this point. Within 3 seconds, the car should lock and unlock doors to verify it is in add mode. (the precise number of times the car locks/unlocks the door is model specific - but it should do it at least once). If it does not cycle the locks, return to step 1. otherwise proceed to step 9.

Steps 9.a. and 9.b. should be started within 40 seconds of completing step 8.
9a: Press and hold the Lock and Unlock key (simultaneously) on the OLD/MASTER fob. (a couple of seconds should pass and the locks will cycle once. If you do not get this cycle, it is likely due to a weak CR 2032 battery in your fob. Replace the battery in your old fob and try again).
9b: Press both the Lock and Unlock key (simultaneously) on the NEW fob. Hold for about 1.5 seconds (several users have reported it being necessary to execute this step twice, if your first go around does not indicate success, try it again and execute this step twice. Please post what worked in the comments below).
9c: Within three seconds, press the lock key on the NEW fob. If successful the lock/unlock will cycle once indicating success (It may take a while for the lock/unlock cycle. I've seen it happen just as I was ready to say, "well, it didn't work". If you wait for a long time (a long time being more than a minute) and get no cycle at all, complete step 10. and test to see if the SKS functions of your new fob work. If they do, pls report that on this thread).
9d. - If you need or want to program another "new" fob, repeat steps 9. a. 9.b. and 9.c. for the next new fob. If done programming fobs, proceed to step 10.
10. To end this programming, open then close the driver's door or put the fob in the slot.

PROCEDURE C
This procedure (steps 1. through 13.) is for black logo key fobs and vehicles without SKS functionality
1. Open the driver door with no fob in slot and the doors unlocked.
2. Insert old fob into slot and remove it twice within 5 seconds.
3. Close and open driver door twice.
4. Insert and remove old fob once.
5. Close and open driver door twice again.
6. Insert old fob in slot and close door.
7. Without pressing the brake, press power button, wait a second, press it again, wait a second, press it a third time to turn car back off.
8. Remove old fob from slot. You'll be in "add mode" at this point.
9. Car should lock and unlock doors twice to verify it is in add mode.
10. Press and hold both buttons on new fob simultaneously for a second and a half.
11. Within 3 seconds, press just the lock button on new fob.
12. Car should respond with one quick lock/unlock to verify that the new fob is all set. If the car responds with two lock/unlocks, that means it didn't work. Either try again, your fob is bad or, you have too many fobs assigned to the car.
13. To end this programming, open then close the driver's door or put fob in the slot.

Here are the part #'s for the fobs:
OEM Fob Part # for smart access is 89994-47061
OEM Fob Part # for non-smart access is 89070-47180.

PS: Practice these steps first (dry run).

I have been editing and improving this procedure for months now and this is the result of many peoples hard work and effort. Thank you to all who have contributed.

Read more: IMPORTANT EXPERIENCE: KEY/FOB Programming Issues | Page 5 | PriusChat

 

I just did this, and it it worked like a charm. SKS functions great!