J-cowboy, Quit trying to buy a boat. It will just become an
anchor for you right now. $20,000 wouldn't be enough money to get anything that would be good for cruising the world and would put you on the hook for dockage and insurance for a boat that you could wind up half a world away from.
Getting into crewing is easier if you don't have a specific place or boat type your interested in. However the more adventurous the voyage the less the pay. An easy way to get into crewing is to start on the tall ships or day catamarans. A quick look through the crew wanted section of wooden boat or sail will give you a good start. Now is the perfect time because all the tall ships are looking to crew up for the summer. There are plenty in the new england area.
Spend the summer on those then start looking for a ride south. There are a couple of tall ships that go to the carip, or the Keys. Also, plenty of private yachts are moved south for the winter. It will be alot easier to get a ride south if you've spent the summer working on a boat. You'll meet more then a few captains and have gotten alot of expeirence.
After you make it to the Caribean, you can start looking for a ride across the pond. As spring approaches, plenty of boats leave the Carib and head for the Med or other European waters.
Along the way, you can look for oportunities to build your boat kitty. You'll learn alot about the differences between Mono, Cat, and Tris. You'll also come accross really great deals.
Again hold off on buying. It will just be something that causes you to turn down a great ride. You'll wind up saying something like " No, I can't volunteer for that trans pac even if you'll fly me out there and back, I've got to come up with $800 to pay my back rent or they're going to seize my boat".