Hmmm lets see with 20 years of inflation, and the way currency grows in this day i woud have to say not more than about $1 or $2 considering that they are about a few cents on the net now.
P.S Summer games is supposed to post your world records online, and anyone can challenge each other making it have unlimited replay value.
You can probably pick up a C64 with a big box full of games on ebay for about £20. Nintendo can't charge that much for them. Loads of C64 games are now freeware and the copyright holder has given permission to download them for free. You can then play them legally on the PC.