Here's an example of pricing using what's available on-line with also the assumption of a 760 FICO and 75% LTV SFR:
Freddie Mac says their average rate today is 3.58% for .50 in fees/points (8/29/19 here:
http://www.freddiemac.com/pmms/)
Fannie Mae's Loan Level Price Adjustments (found here:
https://www.fanniemae.com/content/pricing/llpa-matrix.pdf) Add the following:
LLPA Credit Score (740): .25 in fee
LLPA Product Feature (non-owner): 2.125
LLPA High Balance: .25 in fee
A 3.58 rate at .50 in fee is now 3.58 at 3.125 in fee.
Assuming .50 in fee for .125% in rate (YMMV) a buy down to a 3.25% rate would cost 4.125 in points BEFORE any margins or origination fees specific to the lender! The original post had a loan amount of $565,000. 4.125 x $565,000 is $23,306.25
PS - Using the original 3.58 at .50 "no-cash out" is actually 3.125 in cost. Using the same LLPA matrix, add 1.0 in fee for Cash Out (High Balance) and an additional .375 for FICO score! Now you're looking at 4.50 in costs! To absorb those costs borrowers try to raise the rate for more yield to cover these costs. Even then at a mid to upper 4 rate, that will still leave a point or two to pay out of your cash out.
ARM programs do not have the same YSP as fixed rates which is why Non-Owner ARM loans or Non-Owner Cash Out ARM loans are so expensive.
My .02c