For general welding work the cheapest stuff you can get is A36 structural steel - which is hot rolled mild steel.
If I may suggest a solution to your table needs is buying tables etc. at auction - already pre-made and for much, much, much less then the steel that is in them. Unless you need some custom shapes etc. It just doesn't make financial sense to build your own tables. Even sometimes on Kajiji you can get a workbench for next to nothing. I paid $100 for a 200lbs table and 6" Record vise. $50 for a 500lbs table alone. Etc. Even if you paid $1 per lbs (or less) for hot rolled angle steel there is no way you could come close to these prices. Unless you want a project to learn welding on - that would be something to do.
The cheapest place for A36 in "consumer" amounts is Federal Metals in Calgary (
https://www.federalmetals.ca/we-sell/angle) . If I were you I would look into Edmonton as they seem to be more into industry than Calgary and thus there should be cheap place there as well. Red Deer is closest to you - so check for any suppliers there.
If you want to buy for more than around $500 in A36 then you may get quote from one of the larger distributors.
You can also buy lots of hot rolled steel segments in large quantities at auction. The discussion of a purchase here is for very specific sized pieces for machining purposes - these are not very easily found.