All of my sailing was in fresh water. Sure, salt water is much more corrosive. I actually only spent about $140 that year on line. That replaced both jib sheets, added 250' of 5/8" nylon anchor rode, and 150' of 1/2" 3-strand I cut up and made 7 new 20' dock lines. Let me say it's always been my experience that preventative maintenance and not abusing your equipment will keep corrective maintenance and replacement to a minimum no matter what type of equipment you have.
All boats require basic upkeep, paint, lubrication, servicing, etc. If you own a boat, any kind of boat, you're stuck with that. Of course, sailboats do have rigging and sails. While I have never maintained a boat on salt water, and I hope some of the more experienced sailors on here will correct me if I'm wrong, I imagine that with proper care and regular inspection you can reasonably expect to get several if not many years of useful service from rigging and sails even if you keep the boat in the water year around.
As a homeowner I'm sure you spend money each year fixing things on your house. I know I do. Some years you have to spend more, like putting on a new roof or upgrading the kitchen. I consider it the same with a sailboat. I might go for 7 to 10 years before I may have to spend more that year on new sails. The rigging on my E32 was reccommended to be inspected or replaced every 10 years mainly because the standing rigging is what holds the mast in place.
It's my thinking that if you are living aboard the boat, she is your "house". I can almost bet that the single motor you find on any sailboat will be much smaller than the motors you find on comparable powerboats. That translates to less fuel used annually and lower replacement costs if you should ever need to replace it. Painting, lubricating, corrosion control, and minor repairs are a part of any boat so you will not be incurring any extra work there. With proper care and handling sails last for many years and so will the rigging as long as you take care of it. While anchore line, if you use a nylon rode, will see equal use on both types of boat, sheets for your sails will need to be replaced more often than the sails. For me, I purchased cut-offs from Ebay for my jib sheets but I would imagine that many buy large rolls of line at less per foot then trim to their needs with the remainder stored until more is needed.
You could always take a week off from work, find a boat similar to what you might be interested in and charter it with a captain. That would give you some idea as to whether or not you would feel comfortable on a sailboat, given the differences in hull shape and cabin layout between power and sail boats. I'm sure the captain would be happy to answer any questions you may have and may even give you some instruction in sailing. You and your wife could call it an educational vacation.
I was hoping some of the experienced members might have chimed in on this conversation since I'm sure both of us could use some educating!