Let me first say there are many ways to build this claw machine. I found that making a hybrid CNC/ 3D printer machine makes things simpler mechanically, as these parts are readily available, cheap, and more modular as they are marketed to build a variety of machines. You could definitely go the tradition claw machine route using DC motors for the gantry, which simplifies the power electronics (H bridge ICs) and code to drive them; however, the trade off is it complicates the drive mechanics. Most claw machines have worm gears that drive the gantry, giving the speed reduction and required torque. I prefer a 'bolt-on' approach rather than a custom fabricated mini version for the gantry. I found stepper motors are crazy easy to mount, have a good range in speed (on the low end of speed), and provide more torque than I need (think scalability), so this route was chosen.

COST TO BUILD:

I included a modified Bill of Materials for this machine. The BoM reflects the machine documented here. The total cost is $470. The crossed out items in the BoM reflect the reduced cost version. This removes all the Aluminum extrusion (in place of a wood frame) and some other non-necessities like the LCD and mechanical coin acceptor; reducing the cost to about $210.

I did not expect this machine to cost so much. On the bright side, with a quarter slot it can pay for itself over time and even become profitable. So let's call this build an 'investment'

WHERE TO BUY PARTS:

eBay. If you can wait for things to ship from China, you can't beat those ebay prices.

WHY DID YOU USE ____ PART?

I got the steppers from a USA eBay seller who sells refurb and rebuilt steppers (about $8 per stepper) and I must say the steppers are awesome. Each motor has a molex connector at the base making build/ disassemble simple. The Arduino Mega is a off-brand from DealExtreme (works just fine), and the Al extrusion came Misumi USA (cheaper than 80/20 brand). The cost is pretty high as I buy more than I need and prepare for mistakes (I killed a few ULN2803's and TIP120's already) . It might be better to build this from DC motors, but I went with Nema 17 steppers primarily for two reasons, Mounting them uses a standardized hole pattern, and building a controller for them might prove useful in later projects. This project is easier to replicate (think kit form) with standard parts- Nema Steppers fit this due to the 3D printer market, not to mention all the belts, pulleys and wheels are readily available 3D printer parts. I have saved a few $ by making my own claw, and brackets to form the XYZ gantry. I should stress designing and building the claw was a chore, but well worth it considering the alternatives I tried. I bought (then returned) a few claws as I was thoroughly disappointed in their quality. There are many parts out there for gantries (Inventables' Maker rail...etc) but building my own was cheaper and simpler as surprising as that sounds. I was loathing the task of replicating/ relying-on dimensioned parts from around the web in hopes that everything would "work", but soon gave up on that since just one error in any drawing propagates into frustration after you bought said parts and they just don't fit right. Things have been rather simple with the steppers as I have been sticking to 5mm bore. This 5mm seems to be the most common DIY 3D printer parts, which are everywhere on eBay for cheap.

TL:DR Cost=$470 using Al extrusion for frame, built from 3D printer parts and custom designs from scratch. Total cost is ~$210 if you build the frame from wood.