As the subwoofer is dealing with frequencies below 100Hz (usually about 80Hz and lower), matching the sub isn't so important. Having said that, there are a few speaker packages which need a higher crossover point, sometimes above 100Hz, which not all subs are designed to deal with.
What is more important is getting a suitable sized, suitably powerful enough one for the room size.
FrankHarvey(Dave)........Trying to work out what Sub for my son who has an Onkyo 507, couple of old Wharfdale speakers (6" driver), Acustics centre and 2x Gale rears.... I know, a right mish mash, unfortunately he's strapped for cash at the moment, so a decent budget sub would be good.
You should be able to get a mordaunt short 309 sub for your budget or like one of the others said - a wharfdale which are both 5 star and great for the dosh. Try ebay.
There is one on ebay at the moment on £107 pounds with £20 del and it's the 309'i' improved version, could be worth a punt even if it goes slightly over £150 as they retail at about £180 or more.