boaphile, constrictorsnw, animal plastics, and vision cages all have what you are looking for i think constrictors nw is the cheapest, but boaphile looks the nicest in my opinion, all are cheaper than ricky's enclosures which i think are a rip off. Also the prices listed on boaphile and constrictors nw includes the shipping cost.
for an adult you can probably get away with a 30W by 24D by 11.5H boaphile sells those for $180 shipped
constrictors Northwest has a 32W by 24 D by 12H for $165 shipped
i suggest checking them both out if your looking for a nice plastic cage that'll hold humidity well these are the cages your looking for heres there websites
http://constrictorsnw.com/
http://www.boaphileplastics.com/
http://www.animalplastics.com/
http://www.visionproducts.us/
as for vet visits i took mine into a vet for a check up and to get them sexed and it was only $25. Check ups are usually pretty cheap, its when you have an actual problem they get expensive. just call around see if the vet has any experience with snakes and ask for a check up price.
hope this helps and good luck