2004 Prius with 150k miles. Good Price? 7700 OTD.

Posted this in Newb section, but I think I may get more help here...? Copy/pasting the post below...Mods, please lock/move/advise if you feel it's incorrect. Thanks.
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Need a 3rd car in the family. Never had a hybrid before, but it's starting to make sense now with the gas prices going up.

Didn't go to the dealership looking for a Prius, but saw one on the lot and figured I'd test drive it. It is definitely a different kind of driving experience...one that I enjoyed.

Dealer offer is $7700 out the door for 2004 Prius 150k miles with Navigation and self replaced (used 50k) hybrid system (battery + inverter). Dealer took car to large toyota dealership to get the codes dumped. Car was driven for 200-300 miles more and Toyota technician indicated that no errors showed on vehicle.

Carfax is clean with 2 owners that performed maintenance almost every 3-6 months at the dealership.
Regarding the checklist:
Dealer is unsure about the Transaxle oil change on the vehicle. Most of the Carfax records say "oil change", "maintenance", "battery inspected", etc.

Dealer is getting at minimum 40mpg on the vehicle currently. Dealer has only 1 complaint in past 3 years on BBB.

We currently have a 2000 Corolla with 128k miles running strong (minor issues) and a 2005 Lancer with 120k miles. So the Prius would be the highest mileage car for us.

How much maintenance issues am I looking at? Nothing shows up on the Maintenance screen. I've been doing some reading on this forum, so I think I know what I'm getting myself into...but I'm not a mechanic so I would need to have any future issues fixed by a proper mechanic.

Dealer initially asked for 7900+500 tax,tags,fee,registration. Brought it down to 7700 OTD.
Dealer has another 2007 Prius (base, no navigation, but it does have rear view camera) with 100k miles asking for 9900...but it's a bit out of budget.

Would you...or Should I...
Deal or No Deal?