I need a bike for tooling around parks and on bike trails in the city and for short commutes to the MAX station. I'm not an avid cyclist, so I'm not interested in long or hard rides. Also, I don't want to spend more than 50 bucks.
Basically I don't need a fast or fancy bike. So what do you suggest? What specs and features should I look for?
First, props to you: Maybe you're a more avid cyclist than you think. By actually getting around on a bike, you'll be living stronger than a whole convoy of Spandex-clad Lance-alikes toting snob-cycles atop SUVs.
But Simple, geez! Fifty bucks isn't much to work with. Don't even bother comparing technical specs for that money. You'll need to hit garage sales and thrift stores, and the "features" to look for will be that the bike is (1) all there; (2) mostly rust-free; and (3) fits you fairly well. When you stand over it, you should have at least a couple inches between your crotch and the top of the frame—and you should be able to set the seat height so that your knee is still a little bent even at the bottom of the pedal stroke. (Tip: Sometimes ladies' bikes can be had a little cheaper, and you don't have to worry about crotch clearance.) Try haggling to get the bike for well under $50, and spend the rest to have it safety-checked and adjusted at your neighborhood bike shop.
You know you can bring your bike on MAX, right? That matters two ways: If you bring it along, you'll want your bike to be light for easy porting--and you may feel free to spend more on it, because it won't be sitting out as thief-bait all day.
If you can commit to, say, $150, you'll find relatively light, zippy machines—and competent service—in a used-bike shop such as City Bikes or the Community Cycling Center. Look for a medium-wide, comfy seat, and a handlebar that's not too low. Don't be scared off by a racing-style drop handlebar; it'll be fine as long as it's set high enough to be useful for you. If you can find a bike with full fenders, so much the better; you won't have to pay extra for them when the rain resumes. Good hunting!