I've also been asked to do a t-shirt quilt. I went online and found prices anywhere from $17 to $30 a t-shirt to do a completed quilt which included all materials, quilting and time to do it all. For 18 t-shirts that would $300 at the lowest rate. Go to wimberlyquiltstudio.com and under their quilting services go to t-shirt quilts and check out their prices. I'm doing 12 quilts and quoted a price starting at $250. I haven't heard back from the customer. The quilting would be an overall panto crossing over the t-shirts and no t-shirts with embellishments. Good luck if you decide to do this. I also try to avoid requests for t-shirt quilts.