transmission question Options

[914noob]

I recently bought my very first 914 a couple month ago, and i was hoping you guys could help me out with a few things. First off, i love this car very much and like it more and more every time i drive it, second, i don't know enough about cars to make her run at the best she can. The transmission recently started to grind when i put it into reverse, first when im not moving, and when downshifting from third to second. Just wondering what you guys would recomend for a person in my position. i Want to get it fixed as quickly as possible, but i only have about 500 dollars to spend. Thanks for all your help, your guys site rocks.