World cruiser
The advice in previous posts is pretty good. For the size boat you need the best material is welded aluminum in the modern 508* series of alloys. Aluminum boats can be made very strong for their weight and aluminum is ductile so that minor impacts usually cause dents rather than fractures. Maintenance requirements are low as long as there is no copper, brass or bronze aboard; otherwise corrosion can be a serious problem. A well designed aluminum boat is probably as close to "bullet proof" as you can get (followed closely by steel). Unfortunately, aluminum boats are expensive and you are not likely to find one in your price range.Perhaps next best in sizes over 40 feet, is steel. Steel is less expensive than aluminum but there are substantial maintenance requirements. Medium size steel yachts are much more common in Europe than in North America and you might find one there in your price and size range. Corrosion management is the key with steel boats and it is not just rust on the outside. Corrosion in the bilges and in the cracks along the ribs and stringers can be a serious problem.Third best and probably least costly is fiberglass. You should be able to find a used mass production fiberglass sailboat that will serve your needs within your price range. Fiberglass is strong but tends to lack stiffness and is frequently "cored" with foam or plywood to increase stiffness. A used fiberglass boat needs a careful survey with special attention to the state of the coring. Impacts that will cause steel and aluminum to dent will cause fiberglass to fracture. On the other hand, used boats are abundant and the design is usually more attractive because of the ability to mold compound curves inexpensively.Wood is not a suitable material for extended blue water cruising unless it is epoxy-saturated, cold-molded plywood. Cold molded plywood has roughly the same qualities as fiberglass but it is very labor intensive and hence expensive. It does, however, usually look nicer than fiberglass. Epoxy saturation prohibits rot so the boats will last. While wood has many fine properties, planked boats have the strength of their fasteners, not of the wood they're made of and should be avoided. A sprung plank in the middle of the ocean will ruin your whole day and impacts with floating logs, nearly submerged shipping containers or even whales are likely to pop a plank loose causing a massive leak. Ferrocement is just awful. Heavy and weak it is prone to corrosion of the steel reinforcing which results in spalling of the concrete. It is easy to break and virtually un-repairable. Altering the hull is very very difficult. Don't go there.I recommend to you Dave Gerr's book "The Nature of Boats" for some basic data, Nigel Calder's "Boatowner's Mechanical and Electrical Manual" and his newest "Nigel Calder's Cruising Handbook." These are full of very useful information. If you are likely to sail short handed you should get a copy of John Letcher's "Self Steering for Sailing Craft." This will show you an abundance of ways to make you boat steer herself. Unfortunately it is out of print but is available on the internet through the used book sellers at Borders and Barnes and Noble.