I got a notice to buy-on-line from Barns & Nobel for their warehouse sale. I filtered on Astronomy and came up with a large number of books in the $3.00 to $18.00 range; most books being around $5.00.

http://search.barnesandnoble.com/booksearch/results.asp?SAT=1&userid=2ZVEATY142&sourceid=00409102637656775904&bfdate=01%2D01%2D2004+09%3A02%3A53&brg=y&WRD=astronomy&SRT=R

Jim