There may be someone who is interested in trading in a bike for a newer model and your interest in the old bike may close the deal. You can either work directly with the seller or maybe the dealer will take a minimum markup and sell you the bike. Here you can get a wealth of information as to what bikes sell for. Use a little caution here because the going market might get more or less for a certain type of bike. Of course, when you buy a bike can effect the price as well.
Spring is prime buying time and prices are generally higher.
Mid summer and fall are good times to buy because supply is high and demand is low. Garages are being cleaned out, estates are being settled, people are getting into and out of motorcycling or moving up and down the rung of the motorcycle food chain of speed, cost and sofistication. I made my offer during a massive snow storm. Everyone at the dealership was sitting around watching the snow fall. I'm sure I was the only customer that day.