Prices of instruments through dealers tend to be much higher than those from makers because of the dealers' mark-up. This firm also supplies a number of quality kits, from which my students over the years have produced very satisfactory instruments ranging from crumhorns to clavichords at greatly reduced prices. Commissioning an instrument from a maker will usually provide a greater choice, but will, of course, take far longer, sometimes up to a year or more. Experienced makers ordinarily have a variety of models, and will be able to adjust an instrument to your special requirements. Such instruments can be had from lists published by many of the shops, such as those I mentioned earlier, or from individuals, and the prices are often much less than those for newer instruments.
Instrument auctions can be an excellent source for good usable historical instruments.
Even the more prestigious houses such as Sotheby's, Christie's, and Butterfield's often have a number of moderately priced instruments available. String instruments are more easily acquired this way than winds, since the latter are rarer and command higher prices. Further, the winds are more often apt to be badly worn and are much more difficult to restore to good playing condition. One even sees the occasional historical instrument offered via eBay . Acquiring an existing collection, perhaps from an estate or from a retired professional performer or early-music person, can also be an excellent way to build a collection quickly.