Wow pretty quickly getting talked out of the mongoose. Thats why these forums are so cool you can actually get ideas from real people. I guess my next trip is gonna be to a bike shop. I am scared though. I am such an easy sale! Gotta find a bike shop with some sales people that know what they are talkin about. lookin forward to goin to Boyette again though. Wanna be on a good bike soon!
Visit three or four different bike shops and explain your budget and what you want. Be prepared to go a little beyond your budget by $100 or so.
Also factor in HELMET, gloves, shoes and pedals (eventually), hydration, multi tool w/chain break tool, spare tube, patch kit, Quick Link. These things will ensure you keep rolling while miles away from the parking lot.
You don't have to get them all at the same time, but bike and helmet are mandatory as you need to ride and live to tell about it.