I have the same business model as you and face the same dilemma. Though I am sure that your operation is bigger than mine, and the beef business is a sideline. I ran into the same problem when buying my spring yearlings.
Don't forget that while your costs are going up, so are everyone else's. So if you have to raise your prices you will not be alone. You really have not choice but to raise your prices and make your customers understand the sitiation in the market.
It is unfortunate that although we are buying and selling grass fed beef, we are at the mercy of a market that is somewhat controlled by the price of corn. It doesn't cost any more to feed my cattle this year than it did last year because they are eating grass and hay. But since grass fed is considered premium, the cattle always cost more than conventional, even though it may cost less to raise them.
I was at an auction last week in SW Wisconsin and the grass feed steers were going for as much as $2 per pound.
I think that if the cattle have had a small amount of grain, mixed in with sileage for example, then after about 6 weeks, the affect of the grain has pretty well cleared the system. What is more important is whether they were spread out in a pasture or in a confinement lot.