A Couple of Questions

[John]

First off, are white tree frogs prone to certain diseases?

No. If you provide the right care, your frog is very unlikely to ever have a serious illness.

Secondly, are there behavioural differences between males and females?

Aside from the fact that males call and females don't, very little difference in general.

Thirdly, do they get lonely? Should I get a pair of them?

No. Aside from mating time, frogs are not social animals.

Should I have to leave for a couple of days at a time, is there anything I can do to make sure he is alright while I'm gone? Or should I avoid leaving him alone overnight at all costs?

A healthy, well fed White's should be able to go several days without a meal. There will be differing opinions on this, but I personally would not be afraid to leave a well fed, healthy tree frog for a week without food.

Lastly, could someone give me a general idea of the costs for the cage set-up, as well as the monthly costs for food and other needs?

The set-up costs really depend on how big and "beautiful" you want it to be. On the cheap end of things, I would say US $70 would work, but most people spend $100-$200 gettings things set-up with a nice terrarium, nice lighting, and heating.

Your month to month costs will consist of paying for the electricity associated with the terrarium (fluorescent lights don't use much electricity, nor do heat mats). The other cost will be food. Most people use crickets as food for these frogs and depending on where you source them, they can be cheap or less so. Next time you are in a pet shop, check out the price of a box of crickets to get an idea.