To clarify, plastisol transfers are NOT done with pigmented ink -- the pigmented inks are for doing regular heat transfers, printed from a printer (usually inkjet).
Anyway, a very rough breakdown:
$1.25 - $4.00 per blank t-shirt, depending on type (everyone defines "quality" differently, si it really could be anywhere in that range).
If using plastisol, anywhere from about $0.10 - $3.00 per design, depending on size of design (and thus how many you can put on the same sheet), number ordered at a time (quantity discounts), and colors used (more colors = more cost).
If using regular heat transfers, A good transfer paper will usually run $0.50 to $1.00 a sheet, and then ink costs will range from about $0.10 to $0.75 a print (depending on size of the design and wheter or not you have a bulk system).
Those are the main costs, though of course there are other hidden costs (such as electricty for the press and computer, etc.) They all range quite a bit depending on what you're doing and how you're doing it.