The price is quite reasonable for this at the moment:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=7025317030

Don't pay much more than €70, it wouldn't be worth it. Retail price on these was exorbitant, so they're not that easy to find -- not many people were buying them at retail.

If you're unfamiliar with this course, it has two hardcover textbooks and four cassettes in a nice vinyl case. The Irish taught is an attempt at Lárchanúint (neutral dialect), though advanced students can usually tell what dialect each speaker prefers.

... and readers may be interested to learn that the author of the course, Diarmuid Ó Donnchadha, is alive and well :)

This auction ends shortly, and the price is still reasonable. If you're interested, bid soon!