Hey bud where abouts are you, you could go down to your nearest club and see whats what or maybe go on auto grass NASA site and look at the rule book on there, but will try break it down a little for ya
Strip what you can 
Roll cage - Would ring around for a quote (will need rule book for this)
Electrics - £100ish
Seat- Ebay £50-100
Harness - £75ish
Battery box - Ebay again look for ali boxes ( RSM Fabrications)
Petrol tank - ^^^^^
Race suit - What ever you want to pay
Helmet, goggles - £15-20 each
Other bits- £100ish
Licence- £60
Once your ready to go its a pretty cheap motor sport tbh, Sure i have missed bits out, you can buy a ready to go Micra built for you for £1500, but with time and effort you could have everything you need for around that price maybe less
Hope that helps a little
