Imprintables Warehouse has something called Alloy, that I really love. It is shiny like the "metallic" vinyl, but it is thin, STRETCHABLE, and very soft. I can't recall offhand if it is any cheaper than the glittery stuff
. Where possible, if my customers want giltter, I try to see if I can do the design with rhinestones. It's much cheaper.
I guess your mark-up strategy will depend on what type of profit you need to clear, and whether or not after mark-up, the shirt can reasonably be sold at the final price. I do what I like to call an initial pricing test. I've developed basic pricing for every type of material I use. It typically includes the cost of the item plus shipping, and then is divided by some unit of measurement (sq inches, yards, etc.). I take that price, add 30%, and see if my final price is both reasonable for the product produced, the target market or customer, and worth my time. If not, then I have to decide if I'm going to do the job in a different manner, not do the job, or do the job for very little profit (sometimes that happens, to get a new customer in the door).
Anyway, that's my very simple method. I'm sure others on the Forum may have a more detailed/professional approach.
Pricing Vinyl 
