I have a strong bias here, as I worked as a volunteer and then a "voluployee" in veterinary medicine for almost 18 years. I've seen a lot of preventable conditions tear apart a person's entire collection or cause premature deaths in animals that could easily have been saved if things were caught earlier.
When folks are in the habit of bringing all new animals to the vet for a routine physical exam, baseline bloodwork and a fecal examination it's a very costly thing. But many problems are picked up and treated before they become a full-blown crisis and in the long run these cases end up costing far less money than trying to save a seriously sick animal or replacing a good part of your collection because of pathogens introduced to the household.
If you don't have the money to spend on baseline exams, it's my humble opinion that you really don't have the money to buy the animal yet. Save up, get the animal checked out soon after purchase, have good quarantining and hygiene procedures, and then enjoy your pets thriving.
The Zombie Mama is here!