IMO..people with this type of mentality should not be keeping pets..
i spent $0 on a baby water dragon and paid $236.97 on vet bills in a week. if you can't afford to care for it, why keep it?
just because the animal was "cheap" doesn't make it less worthy of life.
anyway..if it's impacted you should be able to feel the substrate in its stomach by pressing down gently on his stomach with your fingertips. if it feels hard..tube feed him the mineral oil in small amounts and give him a warm bath every day until he passes the substrate.
if it is a parasitic problem, only a vet can help you. a fecal exam shouldn't cost more than $20 and meds shouldn't be more than 30. you'd be looking at atleast a $80-$100 vet bill..which is very reasonable.