unless you get a really good deal then it is less expensive to buy the wide fabric. A simple math check is
3 yds of wide = ?$$
6 yds of 45" = ?$$
Our local $1.99 Fabric Store recently had wide backing at $1.99 per yd. Now that was a deal - so 3 yds= $6.
6 yds of 45" at $1.99 = $12. \\
All their fabric is $1.99 and some good quality. I say this just to make you jealous. But I understand during the bad snow storm here the roof fell in. I believe they are back in business tho.