The first question is Parsons' value is his ability.
Per 36 min:
As the above statistics show, Parsons' is an efficient, lower usage player. He is a career 37% 3pt shooter while shooting 37% of his overall shots from behind the 3pt line. The rest of his game seems pretty middle of the pack. He has decent assist and turnover numbers, with everything else leaving a little something to be desired. Defensively, I honestly don't know. From what I've heard/read, he doesn't always give his best effort, although he seems to have the size (6'9'') and athleticism to be a good defender. Put him on a good team defense, and who knows. I think his numbers show him to be an upper echelon role player, a player that is certainly valuable and one you want on your team, but maybe not one you make a priority to keep.
(P.S. If you haven't seen this, you should take a look. Great comparison of available wings from WFNY.)
The next question is Parsons' fit on the Cavaliers. The current SF situation for the Cavs is...a bit unknown. You obviously got Wiggins (even though Griffin called him a two, I find it hard to believe he won't see a decent amount of time at SF this year), but beyond that there isn't much. Personally I think Parsons' would be an excellent fit starting at the 3 along side Wiggins at the 2. This would obviously move Dion to the bench, but there should still be plenty of minutes to go around.
PG - Kyrie - 36 min / Delly - 12 min
Wings - Wiggins - 24 min / Parsons - 32 min / Dion - 30 min / FA (CJ Miles please) - 10 min
And there can be more minutes to go around if Dion plays the point some, Parsons plays the 4, or of course for injuries.
Now on to the real question. How much do you pay him? Parsons' actual value is probably somewhere from $9-$12 million a year. But the problem with that amount is 1) that Parsons' is a RFA and it would likely take an overpay for HOU to not match and 2) the uncertainty around HOU's situation, e.g. Melo, LeBron, etc. If the Rockets are able to convince a LeBron or Melo to come to Houston, then maybe they are more willing to let him walk. Or maybe they include him in a sign and trade. It's really almost impossible to list all the possibilities.
But back to the Cavs. I'm sure everyone saw David's piece on the current salary cap. Fitting Parsons' into this year's team wouldn't be a problem this year. But with Kyrie Irving's extension looming (hallelujah) and TT's extension/RFA coming up next year, that cap space won't last long. The good news is the Cavs still have a number of pieces to make a big splash next year/mid-season as well. They have Brendan Haywood's $10.5 million dollar non-guaranteed deal, Andy's non-guaranteed deal, Anthony Bennett, Tristan Thompson and Dion Waiters all with large enough salaries to make deal for someone worth the money, but not too large (or untalented) to make the contract toxic. In all likelihood, if the Cavs make a deal for a big name either mid-season or next off-season, it won't be with cap space. It will be with current players on the team and their salaries.
So what's my point? Well my point is that it doesn't really matter how much Parsons' will be making. The Cavs won't have cap space to make a splash in FA next year (barring a sign and trade) whether they offer him a max deal of 4 years and $63 million ($15-16 mil annually), or a deal starting at $10 million a year or $12 million a year. What would 4-6 million prevent the Cavs from doing next off-season? Not to mention Parsons' contract would end the year a certain Canadian number one pick (hint not Anthony Bennett) would be eligible for his rookie extension.
Chandler Parsons' isn't worth $15-$16 million a year, but it's not my money (and Dan Gilbert spends like it isn't his either) so if David Griffin thinks Parsons can help take the Cavs to the next level and that's what it takes to make him a Cavalier, go for it.
Note: I would probably make the same argument for Gordon Hayward, although I prefer Parsons'. If we get rid of Dion, though I would prefer Hayward.