I got my 03 636 brand new as a leftover for 7200 after taxes and everything. I wasnt arguing and I just took what he gave me but I probably could have argued him down a couple hundred bucks. Its nearing the end of the riding season so I would say about 7500 for an 04 and 7000 for an 03. If you're in the country you may have a hard time getting a good price though.
It all depends on the demand in your area. Try calling the dealerships and ask them what their lowest OTD price is. Some dealers will not give you the price on the phone so you have to go meet with them and haggle a bit (knowing that you can still walk away). This is what I did and finally got my 636 for 8130 (including tax/title). You should be able to get a much better deal this time of the year.
It's all about how well you can haggle, and how fast the dealer wants to get rid of the bike. i called a few dealers, most didnt' have the silver that i wanted, but i found one that did about 50 miles away...i talked to the salesman over the phone and went in to see the bike. I had $6850 in cash and showed it to him and just asked "yes or no". He got his sales manager and he said "yes"...if he said no i was going to walk.