I've been using the XM Quickfit life jackets which I bought very cheaply at the London Boat Show a few years back. Although they are not quite the same quality as the Crewsaver, they have worn well and are very good value for money.
Shop around on line and you can find them for under fifty quid
Having said that, for regular use I would probably go for the Crewsaver next time although it's getting on for twice the price as it's not something you buy every day and I prefer the heavier weight webbing and better quality stitching.
XM and Crewsaver both make life jackets with the Hammar hydrostatic release for a few pounds extra too.