Life expectancy will vary depending on the manufacture and model. Don't see why RAID0 should shorten the life span but do you really need it? You'll would also TRIM pass through. I wouldn't say TRIM is a gimmick at all but many of us early adopters got along just fine before it was implemented. Again depends very much on the particular drive as to whether you would see a significant performance degredation over time. Intel drives for example, exhibited very little performance loss in tests. Having TRIM support does mean that you won't have to periodically erase the drive to restore it to 'factory' condition. Almost all current drives support TRIM however and I'd strongly recommend getting yourself a decent drive. I think you might live to regret saving a little on a cheapo.
On your budget you can pick up a quality smallish drive (Crucial, Intel, OCZ) and have change left over for a good secondary HDD e.g. Samsung F3 500 GB.