EDIT. Oops, I just saw that you have a 351 block, I thought at first you had a 302 block with 351 heads. Summit pistons are probably ok if you are doing a beginner/cheap/learning build, some of their stuff is good, some isn't, but their pistons are probably good.
I think with machining, you'll have to check local machine shops for pricing. Ask them if they use a torque plate when they bore, because they should. They will need your block with the main caps, and if they are a good shop, they will ask for one of the pistons that will be going into the block as well so they can do it more accurately. I paid $110 to have my 302 done, but that was about 5-6 years ago. Good luck on the build!