Ferrets you should have more than one: 2 or 3. The advantage to them though is you can adopt a group through many ferret rescues(not as many rescues for gliders). You could also consider fostering first - that way if you decide they're not right for you, you just have to wait until they find a home. You could also foster long-term if vet bills are going to be a major concern as the rescue will cover their vet bills.
Ferrets WILL get cancer. Their lifespan is more like 5-7 - longer if you go through a non-marshall farms breeder though. However, you know that will happen up front. They aren't prone to self-mutilation and hurting themselves like our suggies tend to do. They do require vaccinations yearly(a good time to check for the cancers).
Their diet is easier, but probably costs about the same. They eat a lot! And poop alot! Even if you clean their cage frequently, they do have a slight musky smell. Go to Petco and see if that smell bothers you - yours will NEVER smell that bad on good food(high protein, grain free cat food is best - feeding a mixture of 2-3 types) and cleaning the cage, but that is worst case scenario lol. You can make cage sets similar to those for suggies - they love crinkly things.
You do need to be careful with tiny spaces(like with suggies) and they can get up under furntiure - recliners are VERY dangerous for ferrets - they will get up in there and when you lean back, they're killed :( You need to make sure they don't have access to anything rubber - they like to eat it and it can cause blockages.
They are very playful and can be around most cats and some dogs. Be careful walking them on a leash(they wiggle out of anything!), but the leashes aren't dangerous like they are for suggies. So just keep your eye on them the entire time you have them on a leash.
Another pro I can think of is its MUCH easier to find a ferret vet than a truly knowledgable suggie vet. Either way you go, I'd find a vet first.
My recommendation actually if you want something more temporary until you can get a suggie would be a pair of rats. They are willing to hang out on you for hours at a time, they love toys and exploring, are less messy and much less costly than any of the other pets you are looking at. They couldn't play with the cats, but you can take them out on walks(they sit on your shoulder, you walk lol) They can be taught tricks. Their food is simple and much less expensive. Bonus is, if you get them a very large cage, you could use it for suggies after they pass on(in 2-3 years). And would be easier for one parent to care for if you can't take them back and forth.