You can find a good used gen2 for $6500 if you look around.
There's nothing wrong with a gen1 either, but a gen2 has better brakes, suspension, and more power. As well as no 2nd gear issues, or heating problems at idle(many gen1's need a second radiator fan, the gen2 already has 2).
99 to 01 models also need to be upgraded to an 02 to 07 ecu in order to use ecu editor(flashing software).
Gen1 or 2 both could use better brakes and suspension too, but stock vs stock the gen2 is much better.
Either bike in good shape at the right price is worth buying. You also want to consider what modifications you'de like to do, and what they will cost. If you're like most of us, that never ends.
Better front brake pads and ss lines are a good place to start. Setting the suspension sag to your body weight is free and really needs to be done to any bike. Make the bike stop and handle better first, before getting a few more hp from an exhaust(usaully the first thing people want to add).
Slipon mufflers alone are a good gen2 handling improvement as all the aftermarket ones weigh much less than stock, and that can really be felt riding curves. Slipons are only good for a hp or 2, and you'll never feel that. Buying a bike that already has an exhaust you like will usually save you quite a bit of money too.
As Twotone said already, look out for the condition of the bike, it says alot about how it's been treated. The busa and it's engine have been proven to be extremely dependable with only minor issues.
Good luck with your search and welcome to the org. Everything you need to know is here somewhere.