Re: 5r or sps
A 5R is just over $1000 from just about everyone online, so that doesn't leave much room for the rest of the rig. I say get a less expensive model to have enough money for the gear. That eliminates the 5R or other fancy stuff like the surplus M24 systems Remington is offering.
Just about everyone says get the heavy barrel, for heat and consistency reasons. That eliminates the base SPS you were considering.
Since in your list of "1700 bucks for rifle, optics, and a mount and rings" you didn't list a stock, so I'm assuming that your cousin is just going to use whatever comes on the rifle. That's fine, as long as the stock isn't the weak link compared to the rest of the rifle, accuracy wise. That eliminates the laminated wood and puts the Hogue stocked guns at a big disadvantage, and with that budget you won't be able to get a chassis. So probably not an SPS Tactical, SPS AAC-SD, SPS Varmint, or wood stock models.
The 5R comes with an excellent stock, the HS Precision with the aluminum bedding block, which is also standard on the VS and P series.
Your best bets are going to be:
VS series
P series
Or:
Cheaper Hogue stocked actions like:
SPS Tactical
SPS Varmint
XCR
VTR
with an upgraded and properly bedded stock. (several hundred bucks)
Try to get the rifle set up well for $600-900, leaving more cash for the rest.