Salary cap for us and a regular pop at the spend of other teams is a regular on every rugby forum in the premiership. We regularly hear rumours that Exeter pay well under, Saracens pay over, Leicester don't have one and we clearly can't pay up to it because we don't beat everyone by 30 points with a try BP by half time.
It's all very interesting and entertaining but ultimately there is not too much to chose between the players out there. Unless you are Toulon or Racing Metro and can just watch an international game and buy the man of the match and keep doing so to fill your squad up, it doesn't have as much effect as getting the right blend and coaching to the strengths of the group so for the rest of us salary cap is not as important as intelligent recruitment and good coaching.
Every England selection is surrounded by discussion on 2 or 3 players who could fill each position. For example I think Stevens is a plank but deep down I know there is not much between him and half a dozen other props out there. His skill set fits what was required by 2 top end prem clubs, successive England management and Lions selectors.
Point is wether you pay him £500,000 or 50p he needs to be the right character with the right skills given the right job in your team. Do that for the whole squad and you increase your chance of winning. Get it wrong and even the reputedly most expensive players - Donald and Gray anyone - will be no use at all.