i have a miller cst 250 I used use in my old job quite a bit. It now I've left there I don't really need it anymore. I'm just wondering are these machines desirable? Is it something I can easily sell or is it just better off keeping it?
You can easily sell anything Miller if it's priced right.
It's a 3ph dc stick inverter so it's very desirable to someone with 3ph and I'd imagine very expensive when new.
As for price I dunno. Have a look on eBay in the USA and see what they are fetching and price accordingly. Been a Miller and been an inverter I'm sure you'll gain some immediate interest.