2500 USD it may well be possible. I am in India, and I recently set up a Free NAS based Box with around 16 TB Raw Storage. For Scale OUT Nas, a better option might be using GlusterFS.
This is what we did. I'm providing approximate costs in USD available FOB Bangalore.
8 bay hot Swap Chassis with dual redundant power supply -- 700 USD
(We picked up an expensive chassis)
Intel Dual Core processor + Motherboard -- about 120 USD
8 GB RAM -- 105 USD
2TB drives each 125 USD x 8 -- 1000 USD. (These are 7200 RPM SATA)
This roughly comes to around 2000 USD. We also had invested in an extra PCI SATA card, since motherboard had only 6 SATA ports.
We are using these for a back-up server, not for NAS storage. It works like a charm. We have scheduled writes on to this NAS. And a few reads in a week.
Free NAS Software RAID has no problems. If you have more reads and writes, do use a faster processor. A Quad Core Xeon or Opteron is recommended, and thrown in extra RAM if budget permits. Its also advisable to go for Enterprise SATA drives in such cases, which would cost you around 250 USD for a 2 TB.
I have no idea how much these would cost in Canada, but they cant be way off