Aww bless ya. I know how you feel, by the time it gets to the end of the month I'm in the same boat and just can't afford loads of super free. Aldi has some pretty good deals though.
I used to get really down and dissappointed when I lost 0.5/1/1.5lbs and at first even the 2lbs were a bit gutting. I guess you just kinda get used to it and eventually see any loss as a good thing. I've only managed that very recently though, but its the only way to keep our sanity with all the weight we have to lose.
I think thats the hardest thing about starting 20st plus. Just the sheer scale of the task ahead of us. And it seems okay on the weeks we lose 3/4/5lbs because it feels fantastic, but the slower loss weeks used to make me feel like I had one hell of a long way to go. I guess it still sucks when I get a pound but i've come to accept it more as a step in the right direction.
I'm sure you'll get a bigger loss this week and well done for staying to group. Try Morrisons/Aldi for some superfree, the 1/3rd plate thing is mainly for decreasing calories (as well as the health benefits) so maybe if you can't add the superfree this week try cutting the portions a little, hopefully it'll do the same trick.
*big hugs* and stay positive. You're doing bloody great, i'm sure you'll smash it next week xx