Thing is... you apparently have a history with the school of allowing the children to flout the dress code. So expect that each additional infraction will result in stronger reactions. When your daughter's shoe was eaten, did you call the school and give them a heads' up? Or did you just let your daughter walk blithely into school with out-of-dress-code shoes? Same with the jacket. (And btw, 40 degrees is really not THAT cold. Up here, when they have an emergency drill, they go out in what they have on - which does not include jackets. Doesn't matter if it's 60, 40 or 20 degrees.)
And while they may have turned a blind eye to the belt last year, the fact that there have been multiple times when you and yours have ignored the dress code has ramped things up. What's the point of a dress code if you start allowing kids to ignore it? And no - a belt w/studs isn't black or brown. Any rational person really would understand it means PLAIN black or brown, no decoration.
As for shoes? keds.com - white tennis shoes, canvas, $25-$30 a pair. Buy 2, save 20%; buy 3, save 30%. When you consider your time and gas spent driving to MS, you'd have paid for shipping twice over.
As for choices? Yes, you have choices. Live in a district that doesn't have a dress code. Send your children to a different school. Homeschool. Become involved with the district to make sure that the uniforms put into place are readily available and affordable to the majority of families. Ask about organizing a uniform exchange in the weeks before school starts, perhaps working with one of the local thrift shops. (*) In short - become part of the solution, rather than part of the problem.
(*) And I'm sorry, but if money is that tight? (and I know tight, believe me!) You might want to lower your nose a little when it comes to using clothes from the thrift shops. You - and your kids - might even learn something about conservation and decreasing your carbon footprint.