A single 80GB SSD is better than a thousand 20.000rpm HDDs in RAID0, for the function of the system drive.
With 300 dollars the best Intel SSD you can buy; two X25-V or one X25-M.
Support for TRIM is not essential if you reserve space for the SSD to use internally (i.e. only partition 70GB on a 80GB SSD).
You don't want to use RAID5 on an SSD. You don't want to use RAID at all unless you understand its fundamentals, please have a look on:http://en.wikipedia.org/wiki/RAID