are too much trouble to fit on a budget (i should say too much trouble to fit period)
the 3S while a great engine is also too much trouble to fit on a budget
the 1G is the easiest of them all to put in.
i bought my front cut for $950 and made over $500 back selling parts off it. if u are handy then u can save money on exhaust and wiring by doing as much as you can yourself, the more you do yourself the more money you will save.
you have a pretty good platform for the 1G, u have the EFI fuel tank and pump already, you also have pretty good brakes (my engineer passed my stock RA40 brakes)
HTH
EDIT: look around http://www.toymods.org.au in the articles section and in the gallery/tech docs there is a HEAP of info there.