What Munji said + what SMASH said + what Brad said + buy a lot of stuff used. It's already "depreciated" about as much as it's going to. Save a little extra cash, then move up the food chain.
If you buy a new $3,000 bass today and try to sell it two months from now, you'll do good to get $1,800 for it. If you buy a used bass for $1,500, chances are you can sell it a few months from now for $1,500. If you've saved up $300, you can buy that "new" $3,000 bass for $1,800. Save up a few more scheckels and when you sell the $1,800 bass, you can buy a used $2,000 bass. Now you're into MTD535 territory. Not a bad place to be.
If you MUST spend mega-bucks on a custom, your goal should be to buy a custom instrument that you will keep for a lifetime. Nobody will be willing to pay you what you paid for the custom. Some of the features you decide are "gotta have" will translate to "ehhh" to the next buyer. Until you know what you want your custom to be, play the used market as a tool to play as many different types of instruments as possible.
Peace,
James