"Fleetwood doesn't make toilets - they buy them from Thetford, or other manufacturers, just like you can..."
The above is true. (most of the time)
Look in the owners manual(s) satchel that came with your MH. The make/model of your toilet will be listed on a supplied brochure as well as the installation instructions. A quick google search for the make/model will give you a reasonable retail price. Add an hour of labor (@+-$135/hour) and that should give you a ballpark price. Expect reasonable shop material fees to be added. (+-$50) Add applicable sales tax. Unless there are special unforeseen conditions, (see installation instructions) it should be a very simple job.
Chum lee