I’ve got a good reputation(sometimes 100), but everyone still hates me. I killed some people, but paid for it, or convinced guards to forget about it with speech. I’ve tried going to jail to reset people, but that doesn’t stop anyone from hating me. If I try to sell something the sell cost is 0. I have to pay to talk to most people.
Sounds like your having a tough time of it.
Anyhow, how’s the game working out for you? 
Well, it’s been good. But, I might not be able to do much if I have to pay 200 every time I want to talk to someone and can’t even sell stuff.
You killed people. Thats maximum offence you can do. No wonder people hate you. You have reputation individually in each town/village. It splits further to soldiers,traders and villagers. To raise reputation with soldiers,you have to clean the town periphery from bandits/cumans. To raise with traders,you can only bribe them first and then sell the stuff really cheap,best for free. The worst situation is with villagers. You shoud do quests for that village,but there are not many available. To wrap it up,think twice before killing innocent people or bare the consequences. If your situation is trully desperate,the best would be to return to the save before you commited those serious crimes.