Bikes can be had to fit most any budget, especially if you factor in used bicycles. There's a lot of selection in the $200-300 and up range, but if you need to spend less than that, it's certainly doable.
What you don't need, given what you intend to use it for, is a mountain bike. The large, knobby, low-pressure tires aren't good for riding on the pavement, and the suspension such bikes have is of very little benefit, at the cost of lots of extra weight.
Something in a "hybrid" or "comfort" bike would likely serve your needs best. Skinny (but not too skinny), smoother tires, flat handlebars (as opposed to the "drop" bars you see on more serious road bikes), and either a rigid or suspended front end.