There is a contradiction in the world of woodworking that every hobbyist considering going professional must consider. The way to have fun at woodworking is to make interesting, one-of-a-kind pieces. The way to make money at woodworking is to do the same thing, over and over and over, making the process highly efficient, becoming publicly known for that one thing and selling lots of whatever it is. There are a few highly skilled cabinetmakers who make their living with one-off pieces, but they are the exception and generally charge high prices.
If you believe you are skilled and lucky enough to make it, there is a market for high-end antique reproduction furniture, particularly in New England and the Northeast. A hand-crafted reproduction Queen Anne dining table, built out of fine cherry or tiger maple to the standards of 200 years ago, can sell for upwards of $5,000 or $6,000. A custom built step-back hutch of solid walnut or quarter-sawn oak would go for even more. Building furniture of this caliber requires a lot of patience and the willingness to make a substantial outlay for tools, equipment and materials.
At the other end of the spectrum are pine toys that can be sold at craft fairs and in gift shops. These also take a fair amount of skill to build well, but don't command high prices. Economies of scale are much easier to develop for toys than large furniture pieces. Components such as wheels can be mass produced in large batches, saving a lot of set-up time. Sets of blocks are simple to build and can be made out of off-cuts from other projects, but are great toys for young children. Wooden animals, particularly if they have moving legs or are mounted on wheels, appeal to some parents for their nostalgic feel. The best way to make money with toys is to build a few prototypes, fine-tuning the design each time until the toy is creative, unusual and well-made, and then work on streamlining the process of building it so it can be mass produced in your small shop.
Millwork is any woodworking that is built into a house, such as mantelpieces, baseboards, banisters or door and window trim. Today most millwork is made of cheap materials such as medium density fiberboard (MDF), but there is a market for higher-end houses and renovations in older houses. Particularly if you live in an area with a lot of heritage houses such as Boston or Philadelphia, there is definitely a market for high-end millwork. This type of woodworking requires a larger shop for ease of production because of the lengths of much of the work being produced, but the work itself is less complex than cabinetmaking, because there is less joinery. Millwork involves a lot of tablesaw work and routing of profiles. A woodworker with the right equipment and the right connections can do very well with millwork.