200k is now the low end for elite receivers. IF we paid him that amount, and I hope we didn't, it's fair market value these days. Cripes Walker took down almost 300k per and Ellingson (a low end elite receiver) was around 275k per. Unfortunately, once a couple GMs overpay at a position the rest of the league is somewhat screwed.
Walker got $275k, but has averaged 1500 yds per season (projecting full seasons). So that's the top end.
Ellingson got $250k, and has 4 consecutive seasons over 1000 yds, averaging 1200 yds/season.
SJ Green is on the second year of a two year extension where he will get $210k. Green is older, but is still a 1000 yd man.
Now, Chris Matthews has not demonstrated comparable production to any of these 3, with a single season of 1000 yds. And, he is also coming in late, after the peak of free agency, which likely affects the value a little. Probably worth taking a little hit, just to exhaust the NFL possibilities.
But based on all that, I think you have to figure he is at the $200k mark, and that it is fair value. Its possible he may have backended it a little to help the team with the cap this year, in exchange for a 3 year term. This might be his last deal, so maybe he wants to settle in somewhere.