I was going to say the same thing, the best place for buying large cages cheap has always been Craigslist for me, I've gotten some amazing deals and saved hundreds of dollars on Craigslist, for my Bearded Dragon viv's too. I think people just want to get the cages/tanks out of their homes to make space, and because there are so many of them for sale on Craigslist, they have to basically bail on the prices.
As far as your female goes, I'm sure you've already gotten a Cuttlebone, Mineral Block, etc. inside her cage. Egg-Food is very good for females who are chronic-layers and stressed. Once they get to the stage where they are losing weight it can be very serious, because this is when they are at the most risk for becoming Egg-Bound. So you want to get as much Calcium and fluid in her as possible every day, along with calories, protein, and yes, fat. Egg-Food is awesome just for this situation, it's full of Calcium, protein, and is high in calories. You can either buy a bag of Egg-Food at any Petco for around $10 (one bag last a long time), or you can buy a carton of eggs and make your own, including grinding the shells down and mixing them in.
Keeping them from mating is going to help quite a bit, but keep a very close eye on her, and be watching for all signs of Egg-Binding, as she's very high-risk for it right now, and it's 100% fatal without medical intervention. If she starts panting/open-mouth breathing all the time, if she becomes lethargic, starts sleeping all the time, goes to the bottom of her cage, stays fluffed-up, vomits, or if you see her trying to lay and egg for more than 24 hours without doing so, or you see her at all straining, or her droppings suddenly become very large and messy, these are all signs of her being Egg-Bound. The best thing to do in any of these situations is to get her right to her Avian Vet immediately, but if it happens at night or on the weekend, the best thing you can do is to bring her into the bathroom, along with a shallow container that she is able to sit/lay in, and some Q-tips and Olive Oil. Shut the bathroom door, turn on the shower to maximum hot to fill the room with steam. Put enough very warm water, as warm as she can stand, in the container so that her vent and the surrounding muscles are submerged in the water, and place the container with her in it right into the steam. Keep her in the water/steam for a good 15-20 minutes or as long as you can keep the hot water going. Then you want to use a Q-Tip to coat her entire Vent area, including the very inside ring/opening of her vent, with Olive Oil. It's also a very good idea to keep a heating pad inside of the bottom of her cage for her to go to immediately after the steam bath, so that you can continue to keep the muscles in her abdomen and around her Vent area relaxed at all times, as this will assist her in passing the egg. Provide her with lots and lots of fluids, you may need to assist her by using an oral syringe to do so, unflavored Pedialyte is good to give her. And just keep repeating the steam/bath, the olive oil, and then back on the heating pad until she either passes the egg, or until you can get her to her Avian Vet.
Hopefully you never have to go through this, but being someone who lost a breeder-Budgie years ago to Egg-Binding (and she was taken right to her Avian Vet immediately), I'd rather provide this info than not.