White flies perhaps? Once they get indoors and on your plants, they get out of control but normally will only be annoying and harm only plants. I learned this back in the 80's while "growing my own". In an outdoor environment, the elements keep them under control so they don't do significant harm to the plants but indoors they are a menace.

All of those setups are the kind of elements I was getting at and there are too many shown to list all the ones I like, but you get the idea. As far as money goes, I suppose it depends on where you live and what's available. Substrate for natural looking viv's is the main cost since I prefer reptibark and/or loose coconut fiber but the rest can be quite inexpensive. Try craigslist. Often you can find tanks, dishes, accessories, etc. for very cheap. Just have to keep searching and checking back.