Hi Waxy - welcome to the site.
You've made a pretty tall order. You've basically specified that you want an AC conversion (brushless), and you want to retain trunk & rear seat space. Unfortunately (for your budget), the only way you'll be able to accomplish that is by using advanced batteries (more energy in a smaller package & at the voltage that AC requires).
The DC series (brushed) motor + golf cart batteries is the most cost effective way to do a conversion. And really, replacing brushes every once in a while is no big deal.
I tend to agree with Ben about the concerns over the weight of the car.
Have you spent some time at the EV Album? It's a great place to go in order to get a feel for how much people have spent on their conversions and what kind of specs they ended up with for their time & effort:
http://evalbum.com