Like X-files they also maximized the value they got for their buck by doing as much as they could in Canada (a lot of the crew was Canadian, incl. guest actors (even at least one of the main cast - the general), at least one of the VFX teams, a lot of the postproduction crew. I think they also filmed most of it in BC, but I'm not as sure as I am for the post). Through most of the ten years, not only Canadian companies (especially VFX/postprod) charged on average 15% cheaper than their LA counterparts (even less than that in Montreal/Toronto - Vancouver had a boom of US business then and wasn't as much a bargain. Nowadays prices are similar, since Technicolor has bought many of the top facilities in LA, Vancouver, Toronto and Montreal), but Canadian incentive programs for foreign productions were still at their peak of generosity and to top all this, there was the exchange rate that stood in the 0,65 to 0,75 range for most of those years...

I know nothing of SG-1's budget, but when you look at it, assume they got a lot more value for what they paid for.

Those years of filming/postproducing in Canada at extremely low cost are pretty much gone, among other things which change the situation the CAN$ is worth 1,05 US$ at the moment.