It depends if you build it alone — just one hole remodeled, for example — or whether you are looking for, let's say, 1/18th of the cost of a course. Either way it will be a crap shoot.
An 18-hole golf course in the sunbelt of the U.S. SHOULD cost about $4 million less any structures (clubhouses). Less if a great site, and more if a poor site or a wild and crazy owner. So, figure a couple hundred thousand per hole. Let's give you a range: $150,000 to $300,000 per hole. Par-4 will do.
The National Golf Foundation has lots of publications you can get a hold of — but they are going to be averages if any figures are given.
ngf.org
You might also check out the Golf Course Builders Assoc. of America
gcbaa.org
And,
golfcourse1.com
Good luck.