You can use a "first bike" as a great learning experience, then search for your ultimate frame. You'll note a lot of MBers have more than one ride, and often move the engine from one build to the next.
Take a look in Craiglist, see if you find a good cruiser style bike, which can be modified later. My advise is avoid single speeds and 3 speeds, look around for a 7 speed with wide tires.
NEW? Schwinn has new 7 speeds at around $150, the Jaguars and Pointe Beaches are 2 model names.
Next step up is the Sun's Cruz 7 and other models, about $300-400. If you google "cruiser bikes" you'll see the range of prices and models.
Ultimately, I'm hoping the California Stretch Cruiser comes out with a seven speed w/ hand brakes, the only ones I've seen are singlespeeds w/coaster brakes, and I'm NOT a fan of foot braking.
Front and rear hand brakes have always seemed safer, especially on wet roads.