A mountain bike with front shocks sounds like what you need. In terms of reliability, you really really really should at least get the spring pulley if not the KIP tensioner and the adapter.
Without these two items I was literally about to put my bike up for sale. They are not performance parts, they will just make your bike %1000 easier to ride and probably stop it from destroying your wheels. If you're smart with your shopping you can get a pretty decent set up for $400-500
Bike on craigslist or walmart: $100-$200
A kit: $150
Tools, gas, oil, etc. : $50
Total: $400-500. I bought mine thinking it would change everything but being a beginner like you I didn't have the skill to make those cheap parts work and had to buy parts until it was running. So if you really have to have this to get around I would say, buy the bike you would use and ride it and take the bus if it's too far until you have enough $$ to do it right otherwise you could end being frustrated relying on one of these.