[UPDATE: iSuppli has since issued their own virtual teardown. See Apple can build a $500 iPad for $240.]

Here’s a neat trick. In a report to clients Wednesday, Susquehanna Financial’s Jeffrey Fidacaro published an estimate of how much Apple (AAPL) is spending to build a device that hasn’t been announced, never mind shipped.

Vaporware issues aside, it’s not that big a stretch, thanks to the teardown experts at iSuppli who pegged the bill of materials for a 16GB iPhone 3GS at $180.

Using that a starting point, Fidacaro threw in the extra cost of a larger screen, bigger battery etc. and came out with a total of $347, as detailed in the schedule below the fold.

These costs could vary greatly, Fidacaro notes, depending on

• Storage configuration (1.8” HDD, 2.5” HDD, or perhaps a far more expensive 128 GB SSD that could add several hundred dollars to the cost of the device).
• Which processor Apple uses (e.g., Intel-based Atom or Core 2 Duo, or an ARM-based processor), which could add as much as a $100 swing in costs. Using an ARM-based processor, for example, could lower the tablet’s BOM by $50.

According to a report in the Wall Street Journal Monday, analysts expect Apple to sell the device for around $1,000, at least initially.

Factoring in future Tablet sales, further penetration of overseas smartphone markets and the possibility that Verizon will get the iPhone sometime this year, Fidacaro raised his Apple price target to $250 from $221.

The stock closed Wednesday at $210.97, down 3.41 points (1.59%) for the day.

[Follow Philip Elmer-DeWitt on Twitter @philiped]