They should be around $20 and i wouldn't spend $70 on them since this is the price of a new motherboard with 6 onboard SATA. But generally you should not use the RAID drivers that come with either Silicon Image, Promise FastTrak and JMicron (JMB363). Although these are fine SATA controllers, the RAID drivers adding RAID functionality to these SATA controllers are of bad quality. Performance and reliability might be affected.
Intel RAID drivers are on top when comparing features, performance and reliability. Intel onboard RAID might be especially suitable to RAID0 setups because they offer optional write buffering support which uses your RAM as write-back buffer just like expensive hardware RAID controllers do with their onboard RAM. This is dangerous (crash or power issue can corrupt your filesystem) but if performance is of primary concern and you have proper backups this would be the prefered choice. Second choice would be using software RAID instead, but you cannot boot from a software RAID0 array. If you need to boot from it, you have to compromise.
If you care about reliability and have no good backup and no money to spend on this, you would be better off not using RAID at all IMO.