YOG First question is whether you will be able to do the work yourself. Because what you're talking about is not a trivial job.
The Bristol 40 I sailed on had the galley
stove and sink on the port side near the companionway
and the refrigerator
on the starboard along with a hanging locker if I remember correctly. If the boat you are talking about has a configuration like this, assume you will move the refer and put the chart table there and get rid of the hanging locker so you can put the quarter berth there.
If you're going to have it done professionally, I expect you will end up with at least a four-figure or five-figure bill, depending on how much work has to be done and how much they charge an hour.
Add to that any other upgrades you need for the boat and then compare that to the cost of the 'complete' boat.
IMHO unless there is a really significant cost difference that can't be bargained down, you're better off going with the 'complete' boat.