Joel,
I can not help you with cost in AK. However, personal experience and that of others, build it as big as you can afford. You will not regret it.
I had a 30 x 70 ft shed built on the side of my barn to house / operate a portable sawmill. I thought 30 x 70 was HUGE. Then I started moving equipment into it. First the sawmill. Then the edger. A skidsteer, an offroad forklift, slab racks, infeed deck for the mill... and... next thing I know, I am out of space and still have stuff sitting outside...
Good luck on your project !
.
