A simple way to get a memory cart would be to buy one but I've never found anyone selling them (although I've heard that someone may have ages ago) so there is no simple way.
Even if you had a memory cart you'd have to have a way to program it such as a linker. If somebody massed produced these items together you might be able to get it cheaper than a copier but, you guessed it, they don't.
Since you're on a budget I suggest picking up a used copier cheap if you can find it (which will probably take awhile of looking) or getting the least expensive new backup unit which today is the Super UFO Pro 8.
Of course if you really want to go hog wild you might try getting a Gameboy Color 32Mb cart and building an adapter to the SNES. Who knows, maybe you could even somehow use a Super Gameboy adapter to plug the cart in. Keep us advised of your progress if you go that route. It may take a lot of work but it just might work.