Did the 1st step and bought a bike ( diamondback tekkiya) 
Unfortunately I got ripped off .  
I believe the bottom bracket is to blame as both cranks are wobbling side to side with each other . What do I replace it with (cheap as possible . Make model and link if poss . ) 
Also the previous owner has taken away the gears and has just put a single speed chain on the cog  happy with a single speed bike but surely I don't just leave it like this ??   
I've just started and already I'm regretting it . Please if u can help me . 
Thanks very much