if you want nitro for $350 the Jammin X1 from amainhobbies.com is pretty good they have a $25 off coupon so its $325 + shipping. It comes with everything but nitro in the box and is pretty simple to tune.
Nitros generally around $20-35 a gallon (depending where you live)
only thing is the steering servo that comes with it is crappy and it could use a $30 Hitec 645MG or similar
I wouldn't suggest nitro for use in sand though. Sand can royally screw up a engine if any gets in.
You might be better with a Brushless electric
but most those are around $320ish and need some hefty initial investment in batteries and gear to charge em.