Pah, Who's budget was probably huge compared to Blakes 7's! When B7 began it was given the budget of the show it was replacing, a contemporary police show called Z-Cars!
Its amazing that Who and Blakes 7 look as good as they do.
And not just those shows. For whatever reason, the economy, people not taking SF seriously, whatever, BBC and ITV-produced SF of the 1970s were almost universally given zero-level budgets. And this continued into the 80s.
Check out the first seasons of Red Dwarf. Also Sapphire & Steel. The Tomorrow People seemed to get a bit more money to play with, but not much. I seemed to recall thinking they probably spent most of their budget on the opening credits for that show.
All that said, everything is relative. The only reason US productions of the time looked bigger in budget is because they were shot on film, and film automatically makes shows appear more impressive in some ways. If you want proof, track down any old non-VidFired release of 1960s Who, say An Unearthly Child or The Daleks, and then compare with the recently restored versions that reverted it back to the original videotape look. The videotape version looks cheaper. Even Patrick Macnee's much-maligned early Avengers (and I believe his budget complaints primarily involve the first 3 seasons that were shot on video and even aired live on a couple occasions) look like they had bigger budgets than they did because they only exist as kinescopes now. If they were to be remastered back to video, they'd look really cheap.
Not that North American TV didn't produce UK-style cheap SF at times. The infamous series The Starlost is on DVD and when I watched it I realized the much-maligned SFX of that ultra-cheap show (which was videotaped at a Toronto TV studio probably down the hall from the news desk, just as Doctor Who was at the BBC Television Centre) were no worse, and sometimes were even BETTER than Doctor Who and Blake's 7 episodes of that era.
Being an open-minded viewer, I don't watch old TV expecting the SFX to match what we have today (which is why the cutting and pasting of modern CGI onto Star Trek TOS grates with me so badly). But I do bemoan the fact that the single storyline of the 1970s, or indeed of all of classic Who, that comes close to matching the high-end look of most US SFTV of the time, or nuWho, was Pertwee's first story, Spearhead from Space, which stands as the only regular DW story ever to be completely produced on film (due to some fluke involving a strike, I believe, that forced them to do this). It was an experiment that was never repeated, and even today nuWho is videotaped and transferred to film.
Alex