I like to use pets with armor reduction as passive. Grimm is very cheap, and good for passive (you have to level up Grimm to get the Armor Reduction bonus).

In Happiness bonus, i use 2 pets, Electra when i play normal maps, and Hiberio in Elite maps, both are good and cheap.
(Don't need to have both, i just stack them in other pets, so i can choose when go Normal or Elite maps)

And Arcane Hability, with 1-2m budget, i don't know a lot of pets with good aa and cheap, but i recommend Tadthep, Eterno, Magma...