PLA (Plasma Lyte A) 0.9% NaCl and LRS are generally interchangable for SQ fluids. You can source out which places offer it cheapest. However, it may only save you a few dollars. Ask your vet to order you a box of PLA, they may give it to you a little cheaper.
I was "misremembering" or estimating the cost from my vet, which is only $15.25per bag according to an itemized bill from this summer. In light of this I'll continue to buy from her. But thank you all for the responses--they are much appreciated!