m.ebay.com/itm/191281356897?nav=SEARCH

This cage is cheap compared to others in terms of its dimensions. 60"H X 37"D X 23"W
It says it's made of steel and I don't see anywhere what it is coated in, so how would one determine if it is safe? I followed a link from popular cages on the resources tab so I hope it would be safe.

The cage should be fine but you may find the doors are too small to allow you to put a glider safe wheel into the cage unless you take out the bottom grate and cage pan to put it in through the bottom. The cage is made for birds and is likely to have thinner bars than cages made for small animals.

You might also want to consider the Congo Cage - it is a very sturdy cage with large doors.

http://www.exoticnutrition.com/costsuglca.html

or the same cage from SunCoast which has $10 shipping

http://www.sugar-gliders.com/sturdy-cage-large.htm

So how would you know if a cage is safe ,or if the coating is safe, if it doesn't tell what it is coated in?

I like both of those cages and have seen them both as well as the other suncoast and Madagascar. I just am curious as to how one would determine how a cage is safe if they happened upon a good deal :)

If the finish is safe for birds it is safe for gliders. Most bird cages are lighter weight wire and may have an epoxy coating which is safe, but will not hold up as well as the cages made for gliders that have thicker wire and are powder coated.

Cages that have powder coating hold up well with all the attachments to the cage like hooks for pouches etc. Epoxy finished cages are more likely to chip the finish when using metal hooks for pouches.

The thinner wire of some cages made for small birds may not support side mounted wheels as well. The weight of the side mounted glider wheels might break the wires at the weld connections to the cross bars.