The artwork is what drives the overall cost on these, and simplicity is your friend.
But before you commit to a T-shirt design, think of this in a broader context. This is your opportunity to establish a brand for yourself.
Think of whatever else you might want to use your design on - letterheads, press releases, flyers, videos, premiums and merchandise.
Think of the elements you want to bring to the artwork that will carry over to other aspects of your project, and that will remain consistent from year to year.
Let me throw out an example. Think of the band Cheap Trick. They have kept a number of visual keys and touchstones through their entire career, but let's focus on two -
The checkerboard pattern -
And the logo-type - which has been used in their posters, albums, press materials - everything - since 1977 -
Both are borrowed elements - the checker board from racing, and the logo - likely from an old typewriter.
You see either, and the mind instantly draws the association.
The Moon Eyes logo is the same way - even Penske's truck fleet shares the same logo as the racing team. Lips and tongues? Rolling Stones. Bowtie? Chevrolet. Petty Enterprises? Powder Blue.
The challenge could be to develop a visual touchstone or cue that will carry over and tie together your racing endeavors not only for this year, but for years to come. Simple borrowed elements are easiest, and often easy to manipulate.
These are some example of what I'm doing - and it's borrowed from British TV, Ed Roth and Cheap Trick.
Note that this is a black and white drawing - easy and cheap to transfer or silk screen. The cartoonish effect is brought forth by the scale of the drawing and disproportional sizes of the shifter, wheels, grill - etc.
The logo type I chose comes from the 1960's television series, "The Prisoner". When I chose a number for my car, I chose one with the number "6" in it, and all of my correspondence regarding the car includes the logo type used throughout the series -
The drawing I had made for the logo used the skewed sizing elements of myself - being 6'5", along side the Midget, and while there are those who would argue this is a portrait rather than a caricature, the elements came together in a way that showcases the car well and imaginatively, along with myself, who represents the public face of the team.
The suit? My Mom made it . . .
Anybody can get a cartoon of their car produced - but my thought is that you might want to put into place the elements you can use for promotion, sponsorship, and identification early on, so that your design will serve you and the team for years to come.