i have an old motobecane mountainbike from a couple of years ago and its very weathered. chain, sprockets, cables are all rusted. im wondering if its worth replacing the parts or buy a new bike. which ones could be cleaned and which ones will probably have to be replaced?. if its not worth it whats a good mountainbike to get?( i want to be able to jump off curbs and jump on curbs and ride in grass and stuff because houston bikepaths suck)