I say fix, and fix both specially if there are going to be outside, no need to help add to the cat population out there. There are just SO many other benefits to neutering (cancer/spraying/running away/fighting.. etc... etc...)
The SPCA and sometimes other organizations out there can help with inexpensive spay/neuters.
Around here a neuter is $50, and that's not even a discounted one from a Spay/Neuter group.
Ask your vet if they can get you on a payment plan, call around non profit cat groups, tell them of your situation, and maybe someone can get your cats to their vet for their price.