Yah, AL is cheaper than CU. Compare 250-XHHW-AL to the nearly equivalent 3/0-XHHW-CU; $1.62 a foot for AL vs $3.45 a foot for CU (Dale Electric prices). Both have about a 230 amp rating.
We bought 3 x 620 ft. spools of MCM 250-XHHW-2 AL wire here for running a line off the house to the barn. I have them up for sale on Craigslist, for $2,000. The sheetrock guy cut the rope line that they put in the buried conduit... complete moron. He cut it to fit the sheetrock around the electric panels. I wanted to go after his license and make them fix it and run a new line. The GF refused, after some goon there convinced her it was easy to run a new line... I said if it is that easy, why do they not do it??? Oh, well... it um, well... I said...
So the barn stays on its own independant circuit and we gave up in the idea of runnig it off the house to save the monthly charge to have a separate electric service.