should be around $50 a wheel with the strip/cleaning. rear side wheel weights will work and tire shop can/will do them, just make sure you tell them that up front.
black chrome is much different than just black, way more involved and $$$$$
as far as the caps, those are for you to do, rattle can them with a matching color.
you don't want the coater to do them as they will come back as blobs of melted plastic.
once they spray on powder the wheels will go right into a large hot oven for a while to melt and adhere the powder to the wheels. they will have many different blacks available to pick from, glossy, semi-gloss, matted, textured, just look at their samples and pick what you like.
have fun with it and enjoy when done.
and remember they can do different colors on the same wheel if so desired, they will mask and coat one area then after the first color is cured they will mask that off and color the other areas, very cool effects can be had.
heres one in vegas with a little info.
http://www.powdercoatinglv.com/