Check your oil tank level first, make sure it isnt over full. Check to see how wet/oiled your air filter is. But chances are you did internal damage. if that is the case, it is hard to tell you how much it would cost. It could just be your rings, or it could be the cylinder wall. Anyway, I think you will find that aftermarket pistons and rings will be cheaper than OEM. It isn't hard to change out, but on this machine it is a beotch getting the head off in the frame. You could try and maybe get an O-scope done where they check it internally via the spark plug, but they can't see a whole lot there. If you can't do it, I probably would try to take it to a ATV repair shop that isn't Honda, that way you would pay less for their work, and be able to put in it whatever you want. While that is off though, you should check your valves and guides (as it could possibly be a bad valve guide) and could replace the valves depending on how gunked up those ones are. I think when I priced it out for this, stock OEM piston and wrings were $325, which is one reason I went w/ the big bore kit.
2008 700xx; Power Bomb header with power core 4 exhaust, Power Programmer III, pro armor nerfs, prm products control front and rear bumpers and full skid, 10" ITP rears, ITP Baja's fronts, RZR 2's all the way around, Uni filter, 13t sprocket, CCP steering Damper, DS450 shock swap, Dual Gasser Throttle, bar risers and Moose barkBusters. 730XX kit plus other engine mods!