What do you call decent quality with fun sound to it? Do you want it to have extra bass? Do you want it to have a great midrange? You didn't even mention what types of music you like to listen to. Some of my low priced IEMs that I like very much are the $12 Soundmagic ES18, Sony XBA-1, and Panasonic RPHJE450. The Sony XBA-1 is my IEM with the greatest isolation. it has a great midrange, although some complain that it doesn't have enough bass. I find the bass as well as the isolation is best when I make sure to have it deeply in my ear, with the outer end even with my tragus. It has great detail, and is only around $25. It was originally around $80. The Soundmagic ES18 probably offers the best value of all the IEMs I own. it is one of my least expensive IEMs, but also one of my favorites.
http://www.head-fi.org/t/598627/review-soundmagic-es18-measured
The Panasonic RPHJE450 has 12.5mm drivers. It is ported though, which reduces the isolation. It has good bass slam, but not as much detail as the newer RPHJE355. The RPHJE355 has only 10.7mm drivers, and much less bass impact than the HJE450. The HJE450 is $20 at Panasonic.com.