esotericish makes a good point about the metro cost -- the farther you go, the more you pay. If you travel during peak hours (before 9:30 a.m. or 3-7 p.m.), the price is higher. If you're working and going to school, see if your employer does SmartBenefits, which could pay for your commute. Either way, get a Smarttrip card or you'll have to pay an extra $1 per trip. From Columbia Heights to College Park, you'd be paying $3.45 each way ($2.70 off-peak).
If you do want to live in Columbia Heights, consider group houses. A lot of young people share larger houses and end up paying very little (by DC standards anyway) in rent. That also means shared internet, which saves a bit of money, too. You can find these on the rooms & shares section of craigslist.
Silver Spring actually does have a walkable downtown area, but it isn't super-convenient to College Park because it's on the red line -- so you'd have to take the red line in to Fort Totten and then out to College Park. It's not super out-of-the-way, but not quite as convenient (especially if something happens on the red line, and something always seems to be happening on the red line).
Another thing to look into is the UMD shuttle. I think it's pretty extensive, so even if you didn't live walkable to campus you may be able to get there pretty easily. I think it also goes to parts of Silver Spring, so that'd be one way to avoid the metro costs and time changing trains.