When you water test a used boat, make sure you use the perfect pass, fill and empty all ballast sacs/tanks, check the oil and transmission fluids to make sure you dont see any signs of water. If possible when you have the boat off the trailer, take the chance to have a look at the trailer and bunks.
If buying new, not so much an issue, but based on your stated budget, looks like you will be buying late model used. Which is perfectly fine with the quality of an MC. You should be able to find a heckuva nice X15 for 40-50k.
As for tips to finding, just keep looking. You never know when or how you will find the MC you are looking for. I was looking hard for a Supra when I stumbled onto my MC. It was to good of a deal to pass up, and even though I didn't know it at the time, it was definitely a blessing in disguise. Some one above must have known I needed a MC instead of a Supra. I will never own a boat that is not an MC now that I have one.
Good luck and happy hunting.