My starting point came when a Kaiser System-V enlarger was spotted at a knock-down starting price on eBay. Luckily I was the only bidder and so that became the basis for my copy stand.
Now you can buy new or used copy stands instead of an enlarger. However the asking prices of copy stands are (or at least were) much higher than the numerous, redundant enlargers.
Also the Kaiser System-V does have a specific accessory to convert it to a copy stand - so no home engineering is required to provide the mount for the digital camera. Now finding the Kaiser accessory could be the biggest challenge - but luckily there was an independent camera dealer with one for sale online. True it did cost much more than the enlarger itself - but it was still much cheaper than a copy stand.