Ah Octane that too bad man, ok well lets take a look at the options which may help you decide.
Option 1:
Tear the engine down and take a look at the bearings
Ok if you tear down the engine, it might be worth it for a few things. One you will %100 know what the hell is going on in there. If the bearing is the only thing that is tits up then it is repairable at a fairly reasonable amount of money. It's possible that 3rd and 4th gears are putting some extra strain or in some way exaggerating that dead bearing and the whine is actually the dead bearing itself. I'm kind of leaning towards this solution, while a bitch, if it's just a dead bearing the total cost is the dead bearing and maybe a few gaskets. I know it's a super bitch to do but if you have enough beer and extra hands you could probably do it in a weekend. If that is the only thing thats totally phucked you can replace it out and get another 100K on the bike. I wonder what the hell the previous owner did or did not do to kill a bearing? Shitty oil? Ran it dry? Gas contamination in the oil? Who knows but if your lucky and that is the only thing wrong your in luck(well relatively anyway) While your in there check the 3 and 4 gears if possible, if they look good then you're probably fine.
Option 2:
Buy a used engine and take a bit of a chance.
While this option is a bit scary.(better the devil you know) this has advantages as well. If you get another used engine at a wreckers, you can practically make that bike run forever with the amount of parts you'll have left over from the first engine. Piston pooched? Throw in another, Clutch dead? No probs have an entire clutch assembly. You basically turn into your own Suzuki dealership just in the parts alone you may break close to even depending on how many parts you use from the old engine over the years. I know alot of riders who love having spare engines for their bikes. My friend until just recently sold his original '82 Katana 1100 had a spare and used a bunch of parts from it when things wore out or broke. When he sold the bike he got a little more cash as there was a spare engine with the bike. However this option is expensive and who knows if you are getting a hot rod or a basket case. If the previous owner crashed right outside the dealership after buying it(you guys see that u-tube vid?) then you're basically going to get a brand new engine. If it's in that sort of a good shape you can sell the old one which will offset the cost. However if you get an engine that's been beat every weekend at the drag track and the guy used canola or vegetable oil in there, you may just be inheriting a new set of problems.
I know it kinda sucks but the cheapest and probably best option is to tear it down. According to
www.bikebandit.com if its a piston bearing it's only $13.50 to replace if when torn apart is the problem(possible would cause knocking, main bearing would be whining more). It's possible that this is the issue or are you sure it's the main bearing. The bearing themselves are not that much money they are just hell to get to. If I was in Australia I'd say phuck it Octane I'll bring the beer you provide the food and lets do it this weekend. It possible since this bike shares the same engine as the GSXR1100 I'm sure there are a shitload of parts that can be used floating around out there. If you do fix it and it turns out to be just one bearing you'll thank yourself later. Hell you can get tits up every night at the pub with the money you saved! Also having a look see in the engine also gives you an idea of what kind of service you'll get out of the bike. Other than the bearing it may be pristine inside.