Reddit reviews BEMONOC 3D Printer Parts GT2 132-2GT-6 Timing Belt L=132mm W=6mm 66 Teeth in Closed Loop Pack of 10pcs

Yes, electronics can cost a lot, and many of the telescope manufacturers make things, that when I look at them belong in the 1990s or 2000s, in terms of the way they work, and honestly could have been $400. It's basically the TI calcuator system: https://xkcd.com/768/

People have replaced those control systems, using technology (especially things like improved stepper control) which has come about for various reasons, like 3D printers, and simply faster microcontrollers.

Here's one: https://www.youtube.com/watch?v=tCBgmgc8qiA conversion (I suspect based on that it was using one of the faster controllers, but mine can do fine with an Arduino Mega + Ramps (the cheap controller))

• SVP $300 New
  
• RAMPS kit: (https://www.amazon.com/Eiechip-CNC-3D-Printer-Kit/dp/B07BKVPZ71) $27 (Not the best drivers, but this can be upgraded if you want later probably also want a PPS source, but it can be dealt without. As can the board.)
  
• Motors (Honestly cheaper, but at 0.9 degrees these are a bit better than the normal 1.8 degrees) https://www.amazon.com/0-9deg-Stepper-Bipolar-42x42x39mm-4-wires/dp/B00W98OYE4 2x$20
  
• Pulley for mount (60 tooth) https://www.amazon.com/Timing-Pulleys-Aluminum-Printer-Wrench/dp/B07QH1ZJ9L $8 (2x)
  
• Pulley for motor (16 tooth) https://www.amazon.com/Anet-Timing-Pulley-Aluminum-Printer/dp/B07D294B2T/ $8
  
• Belts https://www.amazon.com/132-2GT-6-Timing-Belt-Closed-Loop/dp/B014QI4PU2/ $12 (I think those are what are needed, I'd have to look again to make sure. I use 110s, but have 20 tooth 1:1, as I use geared steppers, with upsides and downsides.)
  
• Bracket (3D printed) or something made: https://www.thingiverse.com/thing:2278288
  
• M6 screws and 2 nuts (<$5 at local store)
  
• Onstep https://groups.io/g/onstep/wiki/home
  
  So At 408 + a bracket (Easy and simple 3D print or easy to DIY, look at the OnStep Showcase for a number of them.)
  
  Along with a 1/4-20 screw and a dovetail (Oh look: https://www.thingiverse.com/thing:2039785) , and you've got all of the functionality of a one of the Star Adventurers, along with the ability to mount pretty much any telescope up to 8" with a vixen dovetail.
  
  Plus, unlike from what I can tell of almost all commercial ones, they don't seem to compensate for misalignment when tracking. (Ie, they only move RA, not DEC, unless guiding.) Here are some examples of unguided long exposures with dual axis compensation. (Also, He doesn't usually process them, these are per other discussions straight off the camera) https://www.flickr.com/photos/11381732@N08/albums/72157683118306836
  
  Though that uses PEC (Periodic error correction, because worm gears often have high/low spots, so it can be corrected by basically guiding a few times and storing the corrections, which are then replayed). If you want that stored, which isn't included on what I mentioned above, but can be added for the cost of a magnet or two and a hall sensor ( https://www.amazon.com/WINGONEER-Effect-KY-003-Magnetic-Arduino/dp/B06XHG9CYN/ $8 and magnet https://www.amazon.com/Personalized-Multi-Use-Whiteboard-Magnetic-Refrigerators/dp/B075PMV2BC/ $8 ) Otherwise you'd have to retrain it each time.
  
  One thing is that the microcontroller and drivers aren't the most advanced, but you can upgrade them if you want. (STM32 about 3x as fast, but it's rarely needed, except for better alignment is about $60, but add two drivers, so call it a net of +$40 extra but that the kit adds wifi ($6 and a bit of wiring to the original) and a hand controller to it. the faster processors ESP32 and Teensy cost more but are something like 14x as fast allowing better alignment. Mind if you use Howard's Sky Planetarium, it won't matter too much, and it'll be able to process on the computer.)
  
  All new, and unless you have space taken up as your main concern the above setup is in pretty much all respects better than that suggested by dan.