Nike really needs to link up with MF DOOM's estate and rerelease these on Halloween or something. If I struck out at retail, I would probably pay resell, within reason.
You just need a fusion core... but yeah, Power Armors are common later in the game, but there are special star armor just like regular armor. Also, you can give your companions power armor too (except Cogsworth, Dog Meat, or Strong.
I had some really dope black and grey AF1s back in the day... I remember the sock liner and leather both were extra plush. Wish I could remember the style #. My crackhead uncle ended up stealing them after I moved to MI and giving them to one of his wife's kids.