Right, I used to commute backwards and forwards approximatey every 4 weeks and found that if I checked the price of a flight on, say, Monarch, then went and checked the prices on Easyjet, before going back to Monarch again, the price suddenly shot up by exactly £10, even if it was only 5 minutes later. I'm sure they not your IP address and know that if you are revisiting their site, chances are you haven't found a cheaper flight elsewhere, and so they can afford to shove their price up a little.
Ryainair aren't that cheap by the time they add on all their charges and they only allow you 15kgs of hold luggage as opposed to the 20kgs norm. On the whole, Ryainair are a shower of sh!te.