Honestly, get a Honda MT5. I had one when I was young. They are easy to get to high speeds if that's what you wish, They can take ALOT of beating and are cheap and easy to fix.
It's also a very light bike which makes it incredibly fun to race in dirt tracks etc.
Besides, they are very easy to find on blocket and such and they don't cost much at all. Mine did 95km/h+ and only cost me 3,500sek. A bit cheap perhaps, bought it from a friend, but you can easily find a good one for 5,000-10,000sek. Just looking at blocket now i found about 200 of them and almost all of them were under 10,000sek.
And on top of that, due to the weight they are VERY cheap on the gas. That's always a big plus theese days
I had tons of fun with mine and I'm sure you would have aswell. Imo a perfect bike for someone who knows nothing about them and want to have a cheap but yet very reliable one.
Good luck!