Well.. My pet's just lil' over 100hps, and I have yet to challenge them devious meerca bros., I think they have 150hps.. So with an 85str boost, I can do around 50+damage with my current weapons, I think you'd just need to get some good damage weapons if you've got a lowered hit point pet.. Cause in order for me to kill them off i'd need something better, cause with my current I don't know if I could last 3 rounds or more, I don't know for sure.. hmm I'll have to try them out sometime.
As for the foods that give you stat increases, I think Munando Fruit can give you random +hp, It gives you a saying when you feed them to tell you if you've gained any hp or not, I forget what it says as i've never used them, cause I don't consider myself rich enough to take them kinds of chances
idb.finalhit.org - has the listing of the neggs that give stats.. Might have the foods around too, I'm not sure. School and Kitchen Quests are the cheapest for me, I usually don't do the K-quests over 3k, but since i'm doing nothing but training, i've raised it to around 5k since it takes around 15k+ to train at the school. Hope that helps, and always pick whichever suits you best