The G215 replaced the G205. Same interior design, different cabinet design, & the door can be made to swing either way on the 215. Other than that, great boiler. I have one in my in my house and 2 used ones in my garage, that I recently purchased at a very reasonable price. All three units have Reillo burners and burn very efficiently, high 80's. The 205 & 215 are triple bypass boilers and are very easy to clean, no heat transfer pins to get brushes stuck in. They are a very good unit.
It depends on the condition of the boiler, burner & components, and what exactly I get with the purchase of the boiler, what I would pay. For example, the last used G205 I purchased was in excellent condition, housing was not all bent and scratched, oil burner had all new parts (motor, fuel pump, control, capacitor, nozzle & electrodes), backflow preventer, water fill valve, 17 gallons hyrdronic anti-freeze, all 1 yr old. B&G 100 circulator, expansion tank, aqua stat, fuel filter, flow control valve, 1-1/4" copper & paperwork, all for $300. I got a great deal, but I wouldn't have given much more.