You might not know the market value exactly but it's pretty easy to look at the top 10 RTs, see where Wagner falls in and offer him a contract accordingly. Now of course that doesn't mean he'll take it, he may want to be paid as the highest guy. We seen a few guys be allowed to walk because the Ravens wouldn't over pay. If Wagner is set on leaving it's nothing the Ravens can do.
However that doesn't seem to be the plan. Of course I'm not inside the castle and those meeting but I think if Lewis was the perceived option at RT he would have gotten a long look during the Week 17 game when Wagner was out, but he didn't. When Wagner went out of the NYG game, it was Yanda who the Ravens felt was the best option not Lewis(don't think he was hurt yet?. I'm not saying he won't be a good option at RT, but the Ravens clearly view him as a LG and they believe Wagner is a top RT. I'm pretty sure the Ravens knew what type of oline they wanted to build way before it was made public so if Lewis wasn't much of an option at LG I doubt they'd continue to kind of lock him into that spot next to Stanley for years to come. I have to believe that if Lewis was an option at RT, at someone point even if just subconsciously, they would have mentioned his ability to play RT as something to like about him moving forward. But if I remember correctly everything was about what type of LT he could be. I strongly feel the Ravens feel that with or without Wagner they are set on the left side for the foreseeable future.
Lewis may have been drafted as a OT when kicked inside to OG but it seems like RT is only an option in a emergency, must like Yanda