Intro on what it takes to make a cart: well, an eprom burner sure helps!
but all you really need is the burner, a soldering iron, and lots of old cases to cannibalize! I have a schematic and simple instructions I include with every single cart I sell. Buy a cart and I will send you one! Basic idea: (Warning, I am making the wild assumption you know how to count pins on a chip!) take a pac-man cart, a 2532 eprom, and 74ls04 hex inverter. 25 cents, 60 cents, and 20 cents, respectively, when bought in bulk. peel label, remove screw, pop off freq. shielding, desolder chip. save case, screw, and board. Throw the rest away. get 2532 or 2732 eprom (2532 is easier, and I will explain it here) erase chip (you DID buy it used, for like 60 cents, right!?!?) burn new game onto chip (Oystron, Chase the Chuckwagon, Combat, etc) bend up pin 20. I SAID BEND, NOT BREAK OFF!!! It is easiest if you go ahead and fold the thin part on to the thick part as well. Put eprom on board, solder all other 23 pins down to board. get 74ls04 hex inverter. Bend up pin 2. Solder 4 wires and you are done: pin 1 on 74ls04 to board hole 20 that you left open pin 2 on 74ls04 to pin 20 you bent up pin 7 on 74ls04 to ground. anywhere! (but I usually do it at pin 12 of eprom) pin 14 of 74ls04 to pin 24 of eprom (or pin 21, they are connected on board in case you didn't notice) put back in case. TEST!!! Screw closed. TEST AGAIN!!! Print new labels on printer. Stick on case. Mail cart. Pay $5 royalty to game author.