I got my glider from a pet shop, not a breeder for 250 RM from Pet Safari in IPC, Damansara. I know a breeder would've been better, but I wasn't sure where to find reliable ones. I hope you find some experienced and smart breeders as that's a better option.
Also, don't be afraid to discuss the price, even if you have to be a bit stern about it. Sugar Gliders are not cheap, and their supplies aren't any cheaper.
Get one of those big, spacious aviary cages for birds. Normally pet stores will tell you to get a small bird cage like this one:
www.petsandproduce.co.uk/wp-content/uploads/2016/05/86510430ec4c-280x300.jpg
If you ask them for a bigger one, they'll offer you a chinchilla cage. I made the mistake of getting that one. 800 ringgit and it's not even that good. If you're not in any rush to get a sugar glider, though, look for a good one online.
For checkups and vet, you'll need to find a veterinarian clinic that does exotic animals. You'll have to ask them for this information as it's not easy to find out from just checking their page. In KL, what happens is an exotic pets vet will come to a vet clinic once or twice a month, you'll have to schedule appointments in order to see them, otherwise, you'll have to wait a month before you can see them again.
Hope this helps!