I chose components for Phoebe (“PB” or Parts Bin) TurtleBot because they were already available to me in one context or another. But not everyone has the same stuff in their own hoard. As an exercise for completeness, below is an estimate of what it would cost to build Phoebe if parts had to be purchased. Naturally, any parts already on hand can be subtracted from the cost. (The expected audience here is likely to have at least a Raspberry Pi 3 and battery to spare.)

• Onboard computer: A Raspberry Pi 3 with microSD card, case, and DC power supply will add up to roughly $50.
• Laser scanner: LIDAR salvaged off Neato robot vacuum cleaners are on eBay with “Buy It Now” prices of $50-$75 at time of this writing. People living in a major metropolis like Los Angeles can find entire Neato vacuums on Craigslist in a similar price range.
• Motor controller: A Roboclaw with 7A capacity can be purchased directly from the manufacturer for $70. It is overkill for this project, but it was their entry-level product and it was already on hand. Lower-cost alternatives probably exist.
• Gearmotor + Encoder + Wheel: Buying the motors I’m using from Pololu would be $35 each without bracket or wheel. However, similar units including mounting bracket and wheel are available on Amazon for $20 each.
• Caster wheel: A caster wheel can be salvaged off a piece of broken furniture for free. If you have to buy a caster, don’t pay more than $3.
• Battery: The battery pack I’m using are available for $25 each, but it’s far more battery than necessary for this project. A far smaller pack for $10-15 would be sufficient.

Sum total: $238, which still does not include the following:

• 3D printer filament.
• Electrical connectors and wiring.
• Bolts, nuts, and other assembly hardware.

But given room for improvement (cheaper motor controller and battery) a whole package to build Phoebe from scratch should be possible for under $250, less than half of a TurtleBot 3 Burger.

(Cross-posted to NewScrewdriver.com)