Tiller to wheel conversion costs?
Figure it will cost you at least a grand to change to a wheel and probably more like 2 grand when you take everything involved into account.
I would suggest that you sail the boat first and see if it has a helm problem. A lot of boats don''t and a small wheel can be harder to handle than a long tiller when the boat has a strong weather helm. If you install a worm gear steering system the weather helm wont be hard to handle but that sort of steering gear is frequently impossible to install and really costs a lot.
Many times weather helm is caused by a boat that is overcanvased (or improperly tuned). Spending a couple of hundred dollars on a good (i.e., easy to use) reefing system for the main may do you more good than a wheel. Its more a matter of fixing the problem of weather helm in the first place rather than muscling the helm to deal with it. If you use a wheel to hold the rudder off center to compensate for weather helm you are essentially dragging a wide board sideways through the water. That slows you down and stresses the boat.
I had a norsea 27 for 15 years. The boat had a tiller and I was sorry to give that up as I move up to a Tayana 37. The tiller makes autopilots and windvanes easier to install and use, stows out of the way when you are at anchor, and will never surprise you with mechanical problems that could be developing below decks out of sight.
the NorSea would carry a heavy weather helm when over canvassed. I eventually figured that out and put a three point reefing system on the main. At 15 knots I''d put the first reef in, at 20 the second reef would go in. The third was for really heavy weather (35+). As soon as the reef was tied in the boat straightened up, the helm became responsive, and we went faster. The trick is making the reef easy to put in. If its a pain to do you will postpone tying the reef in the sail and either end up doing it when the wind is blowing hard or you will end up sailing around on your ear all the time with a bad weather helm.
Another common cause of weather helm on an otherwise well balanced boat is poor sails. Sails that are stretched and baggy contribute to heeling and helm problems. A nice flat full batten main will frequently resolve weather helm problems.