A meat rabbit's bottom dollar is the flesh they are made of, or, in other words, never sell for less/lb than the meat is worth to you.
Grass feeding to 10 lbs may take up to 8 months, as they grow slower on grass than they do on pellets, and grass alone may not have enough calories for them.
You will very likely end up having to supplement with pellets, grains, or other forage at some point. (Especially spring, fall, or winter months, if your region has them. ) There is a lot of forage feeding wisdom in old RT threads!!
In the US, rabbit kits are usually sold around 8-10 weeks old, and many breeders are happy to buy them at that age, and raise them themselves.
If you are selling for meat, 5 lbs is the standard processing weight, and meat buyers do tend to like them under 12 weeks, as they are more tender at that age. Someone wanting organic or grass fed would probably be willing to buy older.
I personally value rabbit meat at around $4/lb. (As in, that's what it's worth to my freezer.)
A 10 lb rabbit will reliably produce at least 5 lbs of meat, regardless of breed.
So 5 lbs at $4/lb comes to $20.
I do sell purebred rabbits for more than that, but I've never sold a 10 lb adult meat rabbit, even a mutt, for less.