My approach:
Go to your public library (or call first) and see if they have "
Mean's residential remodeling estimating guide" Make sure you use this correctly (read the instructions carefully) and bear in mind that you might not be able to get the prices that they show... it's called estimating

Then I would call at least 2 local general contractors and have them come look at the job. Tell them what you'd like to do and have them estimate the project for you. Be upfront and tell them that you are trying to get an idea of cost but are considering having the work done.
Have a plumbing contractor come and look at the house. Plumbing is a wild card in my opinion and estimates rarely turn out to work. Having a plumber out will firm up a cost that could be the largest part of your budget.
Take a look at all your numbers that you collect - compare whether they are equivilent bids and then check and see if you think it's better to bid the work out on your own or to have a general contractor do all the organization for you. There is some risk in having a general contractor work for you but if you do some homework upfront, check references, check with creditors, and make sure you think highly of the person then it is definitely worth the money to use a general contractor rather than doing the work yourself.
If you are inexperienced in construction, you might at the beginning see thousands of dollars of savings that a General contractor knows are not real dollars. It takes a lot to remodel a home so just factor in the time, stress and current market into your decision.
My personal opinion is that it won't help you a bit to put the home on the market right now, so you may as well begin to remodel - especially if you have funds available. The housing market is glutted at the moment so you will want to wait till at least spring to list the home.
A simple way to arrive at a number for plumbing in Chicago that might be too high or too low in your area is to say that each fixture will cost $1000 in labor to pipe and install. So you simply take your costs of fixtures and add $1000 for each one. Example - shower $1000, toilet $1000, vanity $1000, bathtub $1000... total cost for three full baths = 9000 plus any costs for sewer work or water main. That's union labor in Chicago though.
Good luck. Let us know how it's going.