Atogs are probably the most broken creature type ever printed, and Atog himself is far and away the strongest of the Atogs. While Wild Mongrel is a fine card in some decks, I'm not sure he's quite as strong as he needs to be. Why discard an artifact to get +1/+1 when you can feed it to an Atog and get +2/+2?
Then, of course, there are some cards that might make this a bit better. Disciple of the Vault is a good little creature that can make Atog even more powerful than I already am -- I mean than he already is. I bet Disciple would have good synergy with the deck, and will be great in the mirror match as well.
Then, there's the matter of getting the most bang for your buck. Berserk, of course, would be awesome, but I understand your budget constraints. So how about Fling? You can effectively use it to Berserk and unblocked Atog, and it has the added advantage of being able to let you cirumvent combat altogether. Between Fling and Disciple, Fog is no longer something to fear at all.
Then there is the matter of recursion. You need some way to "break" the Atog's ability, moreso than it already is. How about Yawgmoth's Will? Yawgmoth will let you re-eat all those tasty artifacts. Don't worry -- they're just as yummy the second time around. And, of course, having more good artifacts to eat wouldn't be bad, either. Sensei's Diving Top is nice -- you can stack the draw ability, and then eat it, and still draw a card. And Chroatic Sphere is much better than any egg.
So, those are some ideas. To see a powered version of this deck that I've worked on, just search for "The Atog Deck" in this casual section.
Good luck
