nice looking stuff!
it's great to have these type of prints in inventory so that you can do shows, but don't go in expecting to make money off sales. go in expecting to get exposure. sales will be gravy. price to value your work and to let prospects know that you aren't going to give your products and services away.
i'd suggest $250, $300, $400, $500, and $750. maybe even set higher prices and offer a show discount.
keep in mind, pieces like this are priced differently than what you'd price reprints. these are wall art pieces and have greater value. also, your real market could turn out to be a commercial market. for example, a friend of mine just finished decorating an office building with about 15 huge (5'x6') metal prints; the client saw his work in a coffee shop and it was priced upscale (as opposed to arts-in-the-park give-away prices).
good luck!