Process is:
Look
Tour
Write an offer with a check
Schedule a surveyor and haul out (your cost)
Based on the report you accept the boat and pay the balance or reject the boat for a full refund of the depost. You can propose to renoegotiate too. You lose the costs of the survey always. Some surveyors will discount if you reject the boat before they finish and don't have to prepare a report.
You can find boats a lot of ways the primary internet site is:
New and Used Yachts for Sale - YachtWorld.com
They get the most but all the listings. You can contact brokers to arrange to look at the boats but you can't take them out or rent them. You don't ordinarily get to sail the boat until the sea trial and that is limited. It's best to do some reasearch and I suggest look at boats more and less than your budget so you realize about what your money will buy.
When you write an offer it's not unlike a house. You can offer any amount you think might be accepted. It requires a deposit so the buyer knows you mean it.
You need a copy of the survey report for insurance.