Being a builder with all the tools and knowledge I bet I could do it for that. 2nd hand parts and having expert carpentry skills. I converted my old T5 with all the electrics, sound deadening, windows, rear 3 seater bench, leisure battery, inventor, carpet etc for under £2k. I can buy online the template kit for interior layouts for £100. Buy the lightweight ply and make up units. I used to do upholstery too so can make a seating area.
Don’t get me wrong it may not look like some do it but I’d rather spend the extra bucks saving for my bucket list visit to Bora Bora!
Oh and I know a Polish friend who supply’s and fits pop tops cheap so this all falls into my £12k budget.