Depends on frequencies you want to focus on.
The lower the frequency, the less expensive the coax you can get away with.
If you want performance on 700-800MHz then it's going to cost you.
AT 156MHz:
LMR-400 will lose about 3dB, or half the signal the antenna receives.
LMR-600 " " " 2dB.
1/2" heliax " " " 1.67dB
7/8" heliax " " " 0.9dB
At 850MHz:
LMR-400 will lose about 7.5dB
LMR-600 " " " 4.8dB
1/2" Heliax " " " 4dB
7/8" Heliax " " " 2.3dB
While they do make some "direct bury" cables, this alone isn't enough. You can bury these cables in a trench, but gophers can get it. They'll chew on the jacket and eventually the water displacement gel gets out and the water gets in.
Putting it in conduit would be a real good idea. Since you have to trench anyway, tossing in some pipe won't add much cost, plus it'll protect the cable from rodents and rocky soil.
If you are going to be listening mostly to VHF, then you could get away with something like LMR-400, but if you want good UHF and 700-800MHz coverage, you are really going to have to go with a bigger cable. And that gets expensive.
You could put a preamp out at the antenna and feed it power from your home. The pre-amp will boost the received signal and help overcome the losses. However, you do need to be careful with a preamp as they'll amplify everything in their passband and that can include things you don't want, like cellular, high power paging transmitter, a strong nearby FM station, etc.
You might want to consider keeping the antenna closer to your home and giving up some altitude.