from the sounds of it:
your mother wants the bills paid to ensure continued security of living in her house. so she lets the maintenance of the truck slip due to not affording to do both bills and repairs
what you need to do is to calculate the most priority repair.. im not suggesting steal the entire months income to buy a another truck. but work out whats the smallest amount possible to pay for a repair that will de-risk truck problems. such as making you feel safe to drive it
can you take equipment out of the truck to make it lighter.. is every extra weight of the 'overload' really needed. .. thats one free option
tires and coolant are next on the list.
look to find estimates of costs for not new, but legal replacement tyres(enough tread) and cost out the fix for the coolant problem
is the coolant leaking from the radiator, the coolant tank(reserve/bottle) or a pipe. as that can make a huge difference to cost
negotiate with your mother that fixes are needed. and you have found the cheapest solutions. inform her that if the truck stops working, there is no ongoing income at all, and a new truck is more expensive than the current fixes, so investing a small amount of income to fix the truck, will keep the truck(and you) alive to support getting more income
remind your mother.. money does fix everything, including the truck
doing concession and all the shady thing in life? this is really not my cup of coffee btw, I want to live a productive life not going to do the trivial thing in life for what? for clean house and cooked meal, is it really worth it to race to the bottom?