Hello, fellow Craftster-er!
I know your conundrum verrrrrrrrry well. I look on Torrid and the like all the time, and make a mental wishlist of all the things I would buy if I was rich........or even worse, I see all the awesome things for sale in the small sizes I couldn't wear from the time I was born, LOL.
My first and easiest suggestions would be looking at tutorials on no-sew t-shirt recons or drawing your own designs onto some plain shirts with fabric markers. I took a plain $5 v-neck t-shirt and drew on a retro Elvis design.
Also, there are amazing ideas on here for sewing or tailoring clothing into flattering and stylish new pieces. I made my own Rockabilly wedding dress out of a ridiculous retro leopard-print Mumuu from Goodwill. I also converted a floral "church lady" dress into a hi-low hem, grunge-style dress. Basically, my advice is to play around. I've had my share of recon disasters, but I also have a wardrobe of D.I.Y. gorgeousness that cost me next to nothing. This site is a great place to start, and for lessons on cutting/t-shirt surgery YouTube seems to have a zillion videos to make it easier to follow.