Rules for wedding guests attire question(details inside)

I’ve been invited to a wedding in October and my mother told me that I need to buy a suit and shoes… the problem is that I’m 6’ 5” 272 pounds and need size 14 dress shoes and I barely have the money for a special order… what’s the rule on poor guests wedding attire… my family’s making me take a bus trip to the capital city of Edmonton Alberta and spend what little money I have left for clothes…and I’m going halvers on a wedding present. I’m not friends with either the wife or the groom… but my mother is and she is going with me to the wedding…

my question do weddings always demand suit and dress shoes even for the poor members of the group who can’t afford it?

My mom’s scaring me that I’ll become a pariah If I come in street shoes and suit pants…

P.S. I’m just a guest not an usher or best man