Sure there is alittle play in the girth rule. A tad larger is fine but a snake can try to eat something that is to large.

Another good method of selecting feeders is feeding prey that weighs in the range of 10-15% of the snakes weight in grams.

Ordering online can actually be cheaper especially compared to what you are spending at Petco. The key is to order enough that the shipping evens out the price. I used to make two big orders a year and have a small chest freezer just for my rats.

You may cruise your local craigslist or post an ad looking for a local rodent breeder you can buy just what you need from.

Before I found a local breeder I used Rodent Pro and was very happy with them. They also have Hot Buys where you can score some really cheap feeders.