We bought really heavy duty (10) ga wire rated for in ground (buried) use. In the spring - we live in clay - we'd NEVER get it in the ground in the summer, we buried the cable inside heavy duty black irrigation pipe. We hooked it up ourselves, but then, I've done a lot of wiring. It was fine for about 15-18 years and then we had problems. We were able to use the old wire to run a small rope thru, and then used the small rope to run the new wire thru the pipe. I should tell you - we used the tractor to pull the wire from where it emerged from the ground by the hen house - it was not possible by hand, but we figured it was worth a shot so we didn't have to dig again!!! And it worked!! Our run is closer to 80 feet, maybe a bit more. The wire is pricey, but we bought the best we could find as we didn't want to burn down the coop or replace it soon. The heavier the wire, the less loss along the wire, so in the long run, it's cheaper to use the heavier wire. (It is a PAIN to work with, however)
Depends on what you are willing to do yourself. If you rent the trencher, or use the shovel yourself, there's some savings. I'm pretty sure the electrician would rather just run the wire and not have to fuss with burying it.
Good luck