what sort of size is this garage you are building?
i wouldnt say my price is optimistic. its what i paid! i havent totally finished the build. i still need to tile the roof and clad the exterior to bring it up to a finished garage state, but im eventually going to plasterboard and insulate it to finish it like a room in a home. i want it nice to work in.
i reckon im probably looking about spending another couple of grand. so if i was you i would allow around £10,000 - £12,000 and thats with getting ur hands dirty!!
i have had alot of help from people and i have had to pay them for doing it. ive put alot of effort into this and its not been a build where ive just paid someone to sort it out. ive got my hands dirty every step of the way.