We bought a sail-away with extras last year from Lymm Marina, we had all the electrics, plumbing, bathroom and pump out toilet fitted. I fitted the Kitchen, flooring, bedrooms and storage areas etc, fitted all the other bits such as pipe covers and painted inside. This took a full week off work several weekends and 2/3 nights a week over about 6 weeks. I did it this way to ensure we got the boat we wanted rather than buying a pre-owned boat and then changing it
1 year on I'm still doing all sorts of bits to it, I've painted the outside and all deck fittings are on, but the important thing for me was that we could use it properly within about two months of taking delivery
All costing well within the OP's budget !!