27,5 is a little steep even it is in perfect condition but, IMO, offering 17 will be insulting.
Food for thought and reference: about 4 years ago we purchased a 2004 model year 2400 SC3 - which is the same boat as the SR3 you are looking at except the SC3 has a cuddy cabin instead of bow seats. Our's has the 5.7 (350 Mag) and B3 package and had just over 70 hours on it when we bought it. Boat was (is) in great shape, especially compared to the other boats we looked at in the same price/size range.
After seeing what was being offered in the size and price range - some very sad, un-cared for and un-maintained boats, I was happy to pay the 20K they were asking for the boat and a 2007 model year dual axle trailer. IMO, I would pay a premium for a well maintained boat. Instead of buying a lesser boat, one which you have to make repairs on or replace things before you can enjoy it, you pay a little more for a boat you can enjoy immediately.
As mentioned have it surveyed. If the boat is one that is kept on a trailer then it's not likely there will be any issues, like water damage, with the hull, nor will there be any issues with bottom paint or outdrive corrosion. So the survey will, and should, focus more on the mechanical condition of the engine and drive, and the rest of the systems on the boat. If the boat has been kept in the water it's a different matter - the hull needs close inspection too.
NADA says the average retail price of that boat is around 25K - which will vary depending on options. If that 2400 SR3 is clean as a whistle, mechanically sound, needs almost nothing, and is the right boat for your family, I'd make an offer at 21k and negotiate from there.