What I usually do is the honor system of never trading prepared meals. As already well-known, prepared meals with their quality modifier get to be tremendously valuable. Simply refusing to trade them negates their value entirely, but that's a personal thing, sort of like how I never put more than one weapon into a weapon trap as well, for personal balance reasons.
Only thing you could do is pray Toady One looks at it and writes in code to reduce their value in trade with other civs, but maintain their value when BUYING them from traders. Frankly I don't know why everything trades at a roughly 1:1 ratio anyway; Traders are looking to make a profit off of taking you stuff, they need to buy low in order to sell high. Perhaps in the future The Great Toad could add in a tag or two to materials, say [SELL_MOD] and [BUY_MOD], making things adjustable by modders as to the relative value to traders. Default could be 1 for sell_mod and say, 5 or more for buy_mod, so traders sell that meat for something like 25 apiece rather than 2 but you still only sell it for 2 apiece. This would make the relative quality modifiers for prepared meals a lot more reasonable. May as well write in a custom tag for QUALITY_MOD for everything, so you can adjust how much quality matters to a given item. That would give a lot of flexibility to modders.
That's actually not a bad idea for the ol' wishlist, really. Hmm. That said, I don't think we'll see that in the next couple of years at the rate The Toad is going, considering it's alpha and not beta, balance is not a concern at the moment.