Car Vs. Paid Avast!, Car>>FTW.
It is great as a free product or paid, but in the face of a tight budget, (and not a lot of online financial activity), stick with the free version. The only thing I would consider important to PC security that Avast! Free doesn't have is a 2 way firewall, and there are free offerings for those, or if you have a newer OS than XP, you could just turn on outbound protection of Windows firewall.
Get yourself some wheels!!
(unless you live in NewYork or something, where cars are more hassle than they are worth.)