I know next to nothing about hen weekends, so I'll stick to the bits that I do know about ;-)
The way to find cheap flights with Ryanair is usually to book well in advance (by around 6 months), travel to their less popular destinations (which usually means avoiding the 'sunshine resorts'), travel at times of the year which aren't as busy (i.e. avoiding school holidays) and flying midweek. (Flights at, or around, weekends are often much dearer).
Ryanair flights usually get dearer as time goes by (and the flights start to fill up). They do have occasional special offer periods, when flight prices might drop, but the main bargains are usually to places like Dublin or Frankfurt, rather than to sunshine destinations.
Nobody (not even Ryanair) can guarantee that prices won't go down in the future. (It will depend upon how their computer sees bookings progressing as time goes by). However they're unlikely to do so. (The current economic climate has resulted in many airlines reducing the number of flights which they operate on each route,or even cutting out routes completely. That means that those seats which are left are nearly all the higher-priced ones, with far fewer bargains than there used to be).
You might need to consider an alternative destination. Here's a list of places served from Bournemouth:
http://www.bournemout...ntent/AllDestinations
FlyBe might have some cheap flights out of Southampton:
http://www.southampto...nations+and+airlines/
or from Exeter:
http://www.exeter-air...uled-flights#country1
Chris