The bike you were riding when you were younger may have been a kids bike (much more simple and less expensive).
In terms of finding a new bike... finding a decent/worthy ride for less than $250 is not going to be easy. Even with older bikes that have been well mantained, you will probably be looking at a price similar to that... but it would most likely be worth it. Cheaper bikes are less safe and will not last as long... think of the purchase as an investment.