i have been successful with new sheets but only after 2x washing. i bought 200-count cotton on sale at jcpenny - not their best quality to start with - and after washing it was like butter. i lucked out.
but at joann's they have very wide backing in a limited number of prints and colors. usually $9.99 but if you use the 40 off coupon, well..... that actually feels like printed muslin to me but others think not. i like something tighter than muslin for a quilt that gets used.
please remember that the thread count only means the number of threads per square inch. NOT THE DIAMETER OF THE THREADS. so you can pay for a high thread count and still get mediocre goods.