A simple video on buying insects in South America (Ecuador).
I know many butterflies, in the United States, can be way above $20.00 in price.
Beetles - $40.00 USD
Tarantula - $40.00 USD
Butterflies - $20.00 USD

These are the prices I paid about one year ago in Ecuador, the prices you come across may be higher or lower, depending.
I usually find bugs like these, good quality and great prices, in bazaars and public markets. Ask your hotel manager or guides where the best public shopping places are for these items. Remember to find out if you NEED a license or your purchases may be taken away from you on your exit. (less info)