I am not sure that you can eliminate the things you mention entirely, though they might be specific known items you avoid. Like teak decks replacement say 25K.
Even with a near new motor it cost me about $4k for a new prop and shaft in part because of difficulty removing the old one and access.
Even a new holding tank worked out very expensive like 3.5K because the thru hulls and seacocks needed replacement, plus a few very expensive bits for the head, plus access was very poor making labour cost high.
New anchor chain and warp say 1000, plus windlass at 1700, then modify anchor well and do base for windlass plus stem fitting plus wiring say another 3000. Thats not adding haul out and hard stand charges.
The boatbuilder's advice to me was whatever you think it will cost multiply it by 3 or was it 4?
Even on a very good boat you could well spend 10-20k without there being any major issues, simply because of age wear and substantial costs of everything and boats being hard to work on so labour time and costs are high.
Specifically redoing the interior. I had a quote to redo the laminate roughly a square metre on a u shaped galley $2000. There is a way of repainting it for much less. With some of these things one can learn to do it oneself but there is an issue say in having the tools because of complications like fiddles etc apart from learning the skills of a variety of trades.
At a guess I would think having the interior done could cost a bomb like 20k+ without headlining and upholstery. You might get it for less with veneer and judicious painting.
It really doesnt work to add say 40% to purchase cost because for a near perfect boat it might be 5% for another 100%. The other approach is what is the top price for such a boat? I looked at one in very good shape asking 90k. Sold 81K. Known cost of redecking 25K. One might add 8k for incidentals. Total cost 114K value then 100K. Real value of boat then is 67-75K but that would be considered a bargain.
My figures are NZ $ and costs but it seems like the US figures would be much the same. In short boats cost heaps and much more than you think. Sure the costs are less if you do as much as possible yourself. That involves learning a lot of skills and many times the amount of time you estimate, like 4 days to remove the varnish from a cabin sole. Just saying.