Just some comments. If you are going with direct burial UF is the minimum you should use. Unless you are going to drive another ground rod, 3/C is probably going to be required.
10/3 UF-B Wire w/ Ground
Agreed that single conductor THHN is the way to go if you stick with conduit.
10 AWG THHN/THWN-2 Solid Building Wire - sold by the spool has a 500' spool for $200.
500' is a looong way for 120 VAC. If you use one of the voltage drop calculators, a 10% voltage drop (which is the maximum usually tolerated, 3% is more common), 10AWG is only good for about 8 amperes. Are you sure you want to do this?