How much money do you have? The more you spend, the happier you'll be.
The cheap Russian Gen1 goggles, all basically the same, go for between $400-600, depending on how well you shop around. This is all I can afford, unfortunately.
A decent pair of used American dual-tube AN/PVS-5 Gen2 go for around $900.
A new pair of single-tube AN/PVS-7B, Gen3, anywhere from $1500-$3000, depending upon tube grade.
And a pair of AN/PVS-15 dual-tube Gen3 goggles, water-proof to 60 feet, what the SEALs use, about the price of a new Ford Escort.
I've read that a Gen4 tube has been released--anything with them is probably the price of a new Mercedes.
eBay is a good place to find bargains. If you do a search on Google you'll find a bunch of info on night vision.