As others have said, if you've got a Julio or a Brown or a Green or a Beckham, you pay them. That's just how it works. If you have a future HOF type guy in his prime on your team, you keep them around. And look how few of those guys hit the open market.
What it doesn't really pay to do is go after the receivers who do hit the market. Your Sammy Watkins and Allen Robinsons and those guys. IMO, the cost of WRs right now is inflated above what they're really worth because good QBs are so freaking rare. You are basically stuck with the passer you have whether he's any good or not, and if you've got a young QB, you need to build an offense around him fast before you arrest his development. So in order to develop the Goffs and Trubiskys of the league, and prop up its Alex Smiths, teams are spending big bucks on wideouts. And while guys who can get open and make big catches do help their QB, I personally don't think it's as big of an aid as having a great pass blocking OL or a stud RB. The league seems to disagree with me, but right now I'd say WRs are overvalued and RBs and interior linemen are undervalued. It's not Todd Gurley vs Antonio Brown, like one poster said, right now, the comparison is closer to Todd Gurley vs Brandin Cooks. Both signed for almost identical annual averages, from the same team, weeks apart from each other. That is as close to an apples-to-apples comparison as you're ever going to find. Same price, Cooks or Gurley, who are you taking.
Part of that discrepancy is because the NFL is unquestionably a passing league now, part of it's that RBs are injury prone, part of it's that mediocre RBs can be had for pennies, you get all that. But I think the situation is starting to swing the other way. The league went through a real drought of incoming RB talent from 2009-2012, go on Wikipedia and look at those RB draft classes. They were absolutely horrible. Ryan Matthews, Knowshon Moreno, CJ Spiller, Doug Martin, obviously hyper-bust Trent Richardson, pretty much every 1st round back failed. A lot of the mid round guys did too. But starting in 2015, Gurley, Zeke, Fournette and Barkley have been four blue chip, top-5 type prospects all back-to-back from 2015-2018, whereas there was only 1 RB that went top 10 from 2009-2014 (T-Rich), so the feature backs are finally coming around again. Heck, look at this last draft class too, teams absolutely hammered the 2nd round for running backs. I think we are starting to see a bit of a resurgence just in talent at the position.
On top of that, teams are finding out that RBs can be used to prop up a veteran QB or break in a new one even better than a spendy WR can. And I actually think the Cowboys are responsible for that trend, because we showed the league how to do it twice, with Romo/Murray and Dak/Elliott. Look at Jacksonville, look at NYG - they want their own Zeke. Sure you can get a 4 YPC banger for a 3rd day pick, but good luck finding a stud bell cow who can elevate your QB in the 5th. Gurley set a new benchmark for what RBs are worth because the Rams realize that guys like him are NOT expendable. He's not some committee back you just churn though. He's the engine that makes that entire offense go, he's the guy propping up their 23 yo franchise QB, and so he shattered the roof for RB salaries.
Elite WRs are usually worth every cent you pay them - look at AJ Green almost singlehandedly bailing out Andy Dalton's career for like 8 years - but I don't like what you have to pay for good WRs nowadays. I think we're doing the smart thing by building our line, paying our RB, and moneyballing it with cheap free agents and draft picks at WR.
