00 GLS-problems shifting into 1st, 3rd

I have a 2000 manual GLS 2.0. For the past few days I've been having trouble shifting into 1st and 3rd gears. When I try shifting into 1st from neutral, the stick will go up about halfway and won't fully engage. I have to throw it back into neutral and try again several times before it'll go all the way into gear. I also have a rough shift into 3rd, although that doesn't get stuck (yet, anyway). Clutch pedal is working fine (so far). Any ideas on what the problem could be? Linkage? How much would fixing this cost me? Thanks.

Properly checking cable adjustment can be involved. Get a good manual if you want to attempt it.