If you go to a screen printing shop, they generally charge a set-up fee (my local shop charged $25 per color when I checked a few years back) plus a few bucks per shirt. The plus is that, normally, the screen is yours to keep so you can use it again if you take care of it. The negatives are that they may have a minimum number of shirts for a "run" and they may require you to purchase shirts from them.
If you want to go easy - especially if you want a multicolored image, the easiest and cheapest way to go is to use inkjet iron-on transfer paper. I would recommend paper that says it's for use on dark fabrics - it typically gives you brighter colors and holds up to washing/drying better. It will leave a white background anywhere around your image you haven't trimmed off or non-colored areas within the image though, and I've never come across a brand that really holds up well after a dozen or so washings.
If your design is only one color (or is something that you could do as an outline, then paint in colors by hand), you can make your own screen and screen print at home. I'm including a link to an excellent instructable on the subject. My only suggestion that differs from the instructable is rather than using an embroidery hoop as the frame for your screen, use a sturdy wooden picture frame or cut the frame out of a cheapie painting canvas and staple the fabric to it as tight as you can get it. I've had great results with this method. This option will give you fairly professional results for a relatively low cost. You should be able to make a screen with this method for under $10, and then all you have to pay for on top of that is fabric paint.
I'm not looking for points but i work for a t-shirt printing company. We are the cheapest company in Kansas city, MO and we also did all the david cook shirts that you seen on TV. 816-525-9191 Is the main number. price will vary on what color shirts your looking for and how many colors. black ink on white shirt will be cheaper than 5 colors on a black(dark) shirt. If you don't already have logo one can be made and sent over e-mails. www.freestylegraphics.net is the web site it also has contact info.