[quote name='Dark Lord Greg']well I am going to sell one of my two Nintendo 64, both are in perfect working condition. IS there a way to know the manufacture date so I can keep the newer one? Or is there something I should look for when deciding which one to keep? Both are in about the same cosmetic condition.[/QUOTE]
Be sure to check if one or both have the RAM expansion module, and put it into the system you plan to keep if there's only one. Personally, I would just keep the better condition one regardless of age. N64's like allmost Nintendo consoles are solid, sturdy, and long lasting.
The prices you mentioned on the games you're interested in buying are pretty average for clean cart only copies. Nothing to write home about as they're roughly the going rate/value, so you're not exactly getting ripped off but you're also not getting a deal. Not worth it from a reselling perspective but ok to add them to the collection. I would try to bargain with the thrift store to perhaps get a bundle/bulk discount.