I've been thinking I should go through and make a table of servings of protein and their rough costs.
I consider 30g protein a serving, since that's the amount it seems your body can absorb in one meal / few-hour-period, so it's the amount I try to eat every few hours.
I'm pretty sure the cheapest sources of protein I eat are straight-up protein powder from proteinfactory.com (at $10 a pound it's about $0.75 per serving) and eggs (even at $4 a dozen for the ultra-awesome eggs from the farmer's market, it's $1.33 a serving, since 30g protein is 4 eggs, or thereabouts.)
I know you said you can't eat seafood, but for the sake of completeness, a pound of farmed salmon is $8 from the grocery store here, so that's $2 a serving (a quarter pound of boneless lean meat is about 30g protein.)
So then all meat kind of comes in around there. The good organic ground beef is $7 or so a pound here, so it's a bit cheaper.
Interestingly, while I eat a lot of yogurt, it's pretty pricey, at $12/gallon, which is four servings (I strain it so it's not an unreasonable volume of yogurt, but a gallon of yogurt has 120g protein) it's the most expensive protein source I eat.
I'm starting to make my own out of nonfat milk, which brings it back down to a reasonable level since a gallon of good local nonfat milk is around $5 here, so that's $1.20 a serving.
In trying to put on muscle I try to eat six servings of protein daily. So if on average a serving of protein is maybe $1.20 (I don't eat a ton of the more expensive ones like meat, and I usually make about 3 of the daily servings be the protein powder because it's easy and I'm lazy) then that's $7.20 a day just for protein. Admittedly some of those foods also have fats in them and whatnot, but I generally divide my diet up as those -- the protein sources -- and then everything else is just culinary accompaniment and other necessities like vitamins, minerals, and fiber. So it's mostly fruits, veggies, nuts and whole grains (usually breads) for me. And that stuff is really pretty cheap.
So baseline weekly budget just for protein sources is $50 or so. As far as I'm concerned this is just a basic requirement if you really want to put on muscle, especially 40lbs of muscle in 6 months. That's ambitious and you need to eat a lot of protein every day. You weigh a lot less than I do so you could probably get away with only 4 servings of protein a day and still be putting on mass, but nonetheless, consider where your protein is coming from, what you pay per 30g serving for it, and how many servings you are eating per day, and this is just an unavoidable part of your budget.
Everything else you can do on the cheap. Eat cheap fruits and veggies like onions, bananas, leafy greens, etc. and skip expensive exotic fruits and other seasonal treats, pricier non-local veggies, stuff like that. Take a good daily vitamin supplement if you're worried about not getting all the right stuff. Drink lots of water, don't bother getting any calories from liquids.
That's my advice, I'm having pretty good luck with it.