Yo, so, i got my Japanese N64 on ebay back in october (i wanted to run OoT at the time) for around 110$ (really good quality, with good controller and with the original box), i got my japanese card on ebay as well for 15$ (okay quality, a bit dirty)
If you want to practice, you should use a 3.x gameshark, i got my 3.2 gameshark for 30$ with an expansion pak to add more codes, you can get one for 25 to 35 on ebay, get an original one tho, the 3rd party ones doesn't work, here's a pic of an original one btw:
http://puu.sh/gTzcj/4e07b67c97.jpgIf you have a NTSC one, just do hafus's trick, good luck man ;)
NOTE: get THIS japanese version:
http://puu.sh/gTzv0/2b119513a3.jpgthe other one is the patched version, also known as shindou edition, shindou look like this:
http://puu.sh/gTzRW/f4fa868096.jpgi personally call it the cancer edition lol.