For what it's worth:
I bought a clean 01 SV650 for $2750.00 and have put about $30.00 (other than tires) in performance mods into it (jetting, front spring spacers, thicker fork oil), and just have a flat-out blast on track days. You can spend twenty times as much and have a small increase in fun, but as far as bang for the buck goes, it's been great. Not that the same kind of bargain can't be found on an I-4, but this is just my example. Maintenance hasn't been bad either. All I've had to replace as far as parts going bad, are one fork seal and a regulator/rectifier--$10.00 on ebay for a GSXR650 part part and 10 minutes rewiring it for the SV. Doing fun stuff on a budget is like a sport with me. I could afford better stuff, but for some sick reason, I enjoy it more when I do it on the cheap.
One related issue: tires. I may be wrong, but my own personal opinion is that using crappy tires--not unsafe tires, but street compounds--when you start out, teaches you how to manage traction at lower speeds; kind of like learning on dirt bikes. My observation has been that guys who start out on today's fantastic sporting rubber, often don't learn how to manage small slides until they get spit off. I guess I've gotten off topic. To sum up, I'd say that my approach is to focus less on the hardware, and more on getting out there, having fun and learning better technique each time I ride. Hunting down and passing bigger bikes on tighter tracks is kind of fun too! again, like a sport.