Replacement Key for 2002 Prius - found good source

$135 to $150 is about average for an uncut keyless key from a Toyota dealer, and most automotive locksmiths will not fiddle with supposedly blank keys which were not purchased from a Toyota dealer.

$80 to $90 is what many surplus sellers on ePay are charging for uncut keyless keys, but these can, and often are, either fake, or damaged during manufacturing, or are otherwise unusable.

$135 to $150 for a registered automotive locksmith to actually program your car's ECU to accept that brand-new, Toyota-sold key.

So, a grand total of $270 to $300. Add yet another $40 should you want a duplicate of the emergency mechanical key.

The manufacturer of the special programming equipment gets a substantial cut of the second $135 to $150, and should the locksmith run out of "tokens", he has to "re-up" his equipment to add additional tokens, otherwise his equipment is dead-in-the-water.

The above is for Gen2 and Gen3 full size Priuses. Prius cs can be quite different, depending upon trim level.

Life is a lot simpler for Gen1 Priuses, and a completely different strategy is employed to make "immobilzer" keys.

Figure on $60 for a duplicate of whichever "immobilizer" key you have (Master or Valet), and you can make as many as you want as all will have the same internal code as the "exemplar" key.