Re: How much did you spend on you workstation?
 

USB 3 is plenty fast enough to provide just the same performance from an external disk as an internal SATA disk.

RAID-0 & RAID-5 can provide higher performance than a single disk basically by spreading the I/O load over a number of spindles. If disk I/O is the bottleneck in your system then RAID can get things done quicker.

I use a RAID-5 array connected by eSATA for my current project. It has higher performance than a single disk & even if a disk fails I haven't lost any data. I also regularly backup this project directory to an external USB3 disk (4TB just £140/$210). I have Premiere Pro autosaving the project file every 5 minutes & keep the last 100 copies so if necessary I can go back to a version of the project from 8 hours ago. At night I replicate the working directory on the RAID array to another RAID array.