it is possible to spend thousands but you don't necessarily have to do so. It all depends on how crazy you want to get and how much your bike already needs. The big ticket items are always big bore kits and custom tanks. If you can make the stock tank and sidecovers work for you, and don't mind about the motor being a stocker then you are off to a good start. The more work you do yourself the cheaper it gets since labor is the most expensive part.
Still, with tires, shocks, some form of rearsets, bars, and seat you could get to $1000 in no time but it is spent over time so you may not feel it as much. This is also assuming that your bike doesn't need much beyond regular service items (battery, plugs, oil, etc).
for good shocks check out vipex performance, nice price and set up fot DOHC cb750/900/1100s. Seats - check ebay (1hotwing sells a nice generic bubble back).
Still, with tires, shocks, some form of rearsets, bars, and seat you could get to $1000 in no time but it is spent over time so you may not feel it as much. This is also assuming that your bike doesn't need much beyond regular service items (battery, plugs, oil, etc).
for good shocks check out vipex performance, nice price and set up fot DOHC cb750/900/1100s. Seats - check ebay (1hotwing sells a nice generic bubble back).