Second on the muslin
check to see if your local fabric store has a SUPER CHEAP REMNANT OF AWESOME section, where you can get different fabrics that resemble the most of the characteristics of stuff you wanna work with i.e. Knits, wovens, heavy versus light fabrics, trying out patterns. etc. sometimes if you are going to work with a knit for the costume, Muslin just won't cut it as far as practice.
But for beginners, second Coupons being your best friends and Watch for bigger holidays, as sales at mass retailers and even the family owned joint I work at have sales correlating with big holidays...next one coming up is MLKjr. or Presidents day sale in Feb.
Keep you eyes peeled, and if the store has mailers or catalogues, you can sign up every now and then they send coupons.
Katsucon 2014, Otakon 2014