There are already dealers who will accept scanner trade-ins and put the money towards your new equipment purchase. Main Trading Company and Zip Scanners are two vendors that currently accept trades. While these programs may seem easy and convenient to get some extra money for your new equipment purchase, you probably would do much better money-wise by selling your scanner here in the RR classifieds (probably the best choice) or on eBay, Craigslist or Facebook Marketplace.
As an example,
Zip Scanners is currently offering only $300 for an SDS100 trade-in. If you follow that link, you will see that they also deduct $$$ if your scanner does not meet all of their listed criteria. You also have to pay the shipping charges to get the scanner to them for their evaluation and they will NOT pay any extra money for DMR, NXDN, ProVoice or Waterfall keys that are already installed.