The XW series replaced the XL eyepiece in Pentax's lineup a couple of years ago. They are extremely similar optically, except the XW has a slightly wider field of view (70 degrees vs. 65 degrees).
The XW also has a couple of other improvements -- most notable the ability to slip off the rubber eyecup and directly thread on a camera adapter. But, otherwise, they are extremely similar. For those of us on a budget, finding a used XL at a place like astromart.com is a nice alternative to the $330 XW. You can often find XL's for sale there for around $200.
In your desired range, the XW is available in 20mm and 14mm, and the XL is available in 21mm and 14mm. Any of the four will provide spectacular views on your PF-80. A 20mm ep will provide 24x magnification, the 14mm will provide 34x.
Here's a nice article comparing the XW10 to the XL10.5, as well as general thoughts on the two lineups (note, this is primarily directed at astro use):
http://www.cloudynights.com/documents/pentax.pdf
