The obvious choice for cheap birthday party invitation printing is PsPrint, which boasts a wide selection of premium papers at affordable prices. No matter which printer you choose, make sure they likewise offer premium papers so your birthday party invitations look great and have long-lasting durability (it's amazing how quickly poor papers can be torn in the mail). You should also choose a printer that can provide envelopes and even address, stamp and mail your birthday party invitations out to your mailing list for you so all you have to do us upload your design and forget about it.
There are many options for printing great-looking birthday party invitations, but the most economical way is to print on a premium 16-point gloss paper. You'll also want to stick with a standard size such as 5-inch by 7-inch to keep your birthday party invitation printing costs cheap; however, when it comes to colors you can go with full color since this option really costs little more than black and white yet has much more bang for the buck. Beyond those options, you would be wise to get matching envelopes (also cheap) and have a hardcopy proof sent to your doorstep before you actually print the entire run. The last thing you want is for a mistake to go unnoticed until your invitations are printed, when it will be too late or too costly to make changes. A hardcopy proof does cost a few dollars, but it's cheap insurance that the rest of the run will go off without a hitch. Pass your proof around to friends, family members and co-workers so you can get more than just one set of eyes looking it over for errors.