If you are looking for a cheaper alternative to the airhawk, which should do the same job then try these guys:
http://www.danmedicasouth.co.uk/category/motorcycle-seat-pads/ £59 for what looks like a decent cushioned seat.
I have the gel seat already, and just ordered the bead seat for my long flight back home, I may just use it on the bike as well
They have just changed the M/C page - I went to order online as was annoyed to find the postage was £12! I sent them an
e-mail and was told it should be £4.99 - so best to phone up your order as the website isn't correct.