If they are on the terrarium, just just taking the glass out. On PVC cage you can probably still get the glass out by lifting up an pulling the bottom out. With the lock on.
This also is a great thought. My enclosures have a lip the glass fits into on the side. I just trie mine and it catches on the inside before it clears the track. But it may work on other designs.
Before you drop $$ on a locksmith, try picking the lock with a paperclip. It's worked for me a dozen times with this type of lock. You don't have to do anything fancy. Just stick the rounded edge of an appropriate sized paper clip in and try turning it with a pair of pliers. Worth a shot anyway. You'd be surprised how cheaply these locks are made.
If you just want to get the lock off, drill through the cylinder with a 1/4" bit. I've done it many times before when breaking into filing cabinets; it takes maybe 2 minutes of drilling. I'd use some cutting fluid to help the lock from getting too hot and cracking the glass.