I went to the local quilt shop with the t-shirts I have so far and asked the owner if she ever quilted a t-shirt quilt. She said "no". Upon inspecting my shirts she said she wouldn't suggest quilting them anyways because to quilt around the design would leave a lot of space in-between and quilting through the heat seat designs might ruin them. Plus, stitching over the designs would look kind of tacky as you'd notice the black stitching over the images rather than the images themselves. So she suggested tying the quilt and ended up leaving the store with a skein of black Perle embroidery floss (being that it would be stronger than the regular embroidery floss).
Great because it means I won't have to send the quilt in anywhere and pay more (funny because I haven't been exactly concerned with costs thus far as I've paid over $160 in shirts, interfacing, and binding fabric with giving a hoot about it). But I haven't tied a quilt this big before. I tied my first quilt...with yarn with a big blunt yarn needle through the flannel 36"x36" quilt I made. I only made about 8 ties as I only tied the red filler squares in-between the black and white nine patches. I'm surprised those 8 ties have actually held up despite being used by my God son since he came out of the womb (was his favorite blanket 'til he got into superheroes and got Spiderman and Superman fleece blankets). But I sure can't get away with just 8 ties on this t-shirt quilt (which is going to be 80x80) and I haven't tied a quilt since the first one (which is going on 4 years ago).
I'm open for any suggestions on how to tie a quilt.