What does it cost per unit for a 7" or 12" pressing?
Jesse, it varies hugely depending on the weight of the vinyl, and especially on the packaging.
You might be able to get super-basic 12" vinyl in a plain white or black sleeve with a punch-out so you can read the label on the disc (but otherwise, no printing on the cardboard sleeve) for $2,000 for 500 discs, or $4 each.
Stepping up to 180 gram vinyl, or colored vinyl, and full-color gatefold packaging with any kind of printed, color inserts at all, you could very easily climb beyond $6,000 to press 500 discs with packaging... $12 each.
It's not hard to find a quote for a shorter run, say 300 copies, with full deluxe options, that pushes the unit cost over $20 each!
From what I've seen, the difference between 7" and 12" is similar to the difference between mini-CD and regular CDs, which is to say not as much as you'd think. If you're pressing large numbers (thousands) then 7" end up being quite a bit cheaper. I seem to recall playing around with the quote generator at the web site of one of the big vinyl pressing places, and coming up with a simple, plain paper sleeve 7" that came close to $1 per unit in larger quantities. There may be ultra-cheap shorter-run 7" pressing options but I haven't really been looking that direction.