Oak Larders to 74 con (cost me from 19-70 about 5-10m all told) then from 74-99 (oak?) dungeon doors. Not too sure how much dung doors cost, but you can easily figure that out by using the tip.it con calculator.
The length of time would be about a week at the very most.
19-70 took like 3-4 hours (5 with getting the SC hammers (needed 3-4)).