It's entirely up to you. If money is tight and you cannot afford it I wouldn't feel bad about it at all. I've never done either for any of my cats, other than when my one cat got his leg amputated I did an inhouse blood panel just since it was a longer surgery vs. a spay or neuter..
I worked at a low cost spay/neuter clinic for quite a while as a vet tech until I got laid off a few weeks ago.. what I can tell you is we did roughly 10,000 animals there a year with just the basic of basic equipment.. no monitors (we were the monitors!), no fancy bloodwork machines or whatnot. The majority of the animals that came to us had never been to a vet before and were of varying ages from 2 months to 14 years. All in all we would loose maybe 10-20 animals per year, the majority of which had totally insane underlying conditions we couldn't have known about until a necropsy.
Generally spay/neuter is quite safe
So wishing you all the best tomorrow morning!