Welcome to TBN, Curtis. This is a great site to find answers to all of your tractor related questions. The debate between rear finish mowers and mid-mount mowers is a common occurance here. So common, in fact, that if you do a search for rear finish mower (RFM) or mid-mount mower (MMM) you will find more information and opinions than you will probably want to read. I'll summarize my understanding:
MMM
Pros - Good manuverability if you have obstacles on your property (like trees), don't have to continuously look behind to check on your mowing.
Cons - More difficult than RFM to mount and remove, more expensive.
RFM
Pros - Easy on and easy off, cheaper than MMM. Good for wide-opn spaces.
Cons - Difficult to negotiate around tress, fences, etc. Constantly twisting your neck to check behind you.
Costs - Expect $500-1000 difference for similarly sized mowers. I've been given a price of about $2400 for a MMM. RFM's maybe $1500 - $1700. Not sure but I seem to recall figures in this range. I'm sure you can find examples of each that are more and less than than the figures I mentioned, thus narrowing or widening the cost difference between the two.
Good luck.