Better call around and try to get a better price on that man. I had my new Yamaha 150 installed for $125 from a dealer but all they had to do was hang it and hook up the existing oil tank and existing controls. $2500 to install sounds WAAAAAAY high to me.
Also, I was told that you have to have the dealer install it in order to validate the warranty, but according to the last dealer I spoke with they were willing to let me install it and they would "check it" afterwards for a small fee in order to validate the warranty.
Just something to think about - by the way - we all hate you for getting a new 4-stroke!! It just ain't fair!
About your question, unless you get hold of a "leftover" motor (new previous year's) I doubt you'll see much of a drop in $$ between now and winter.
Good luck Buckley and keep us posted!