Automatic Trans Problem

[drifts14x]

Hey there, this is not 240SX Specific, but I figured that one transmission is basically like any other, so here it goes... I have a Mazda MX-6 that I can buy for $300 as a beater while I put on my turbo and silvia headlights. The car runs, transmission works in reverse, but in drive, I have to rev to 3k in order to get it moving. What do you guys think is wrong, can I fix it myself, and how much do you think it'll cost. I'm just trying to figure out whether or not this is worth the time. Thanks again.