300 yes.... don't even think about it. But, there is nothing wrong with a 440 to learn on. I had one back in the day... and it would pull my 200 Lb butt around without an issue.
The old Kawi hulls kind of suck.... but they are cheap. So... if you find a nice clean one for $400~$600... go take a look at it. FYI in 1981, there were some design changes... so try not to find anything older than around '82.
The "SX" hulls are going to be more expensive.... and they really don't handle very good. I don't know if I would pay what people want for them. But... there was a transition Sx550 (late 80's, to very early 90's) and it was basically the old hull, with better sponsons, fitted traction mat, and a rear exhaust. Those still go cheap.
Honestly.... it's hard to beat a square nose SJ. If you don't get into a hurry.... you can find them in good shape for under $1k. My last one was bought for $600.... and it was great !!!! Unlike a regular jetski... the standup's don't see a lot of full throttle time, so as long as they were maintained... they will run well. the square nose will have either a 650 or 701 engine. Either are SUPER reliable.
Wait a couple months... and every old stand-up, that's collecting dust, and isn't getting used, will come out, because people will want to free up some X-mas $$$.
Here's my $600 champ: