I know for sure Colligan makes a great accordion. Colligan is cheaper on his prices. You should find out exactly how much your friend bought it for before you buy it for 2000. However, seems like you cant go wrong with the Acadiana.
My first Cajun Accordion was a Leland Colligan Acadiana. I find that his accordions have a characteristic and recognizable sound. All in all, a good accordion, but $2000 still sounds a bit high...
You can get a brand new accordion from Leland Colligan for about $1,600 to $1,900 so there is no way I would pay $2,000 for a used one. $2,000 for a used Martin, Acadian, Falcon, etc is even too high. I would value a used Acadiana in good condition to be around $1,000 to $1,300. You can get used Acadians and Martins in good condition for about $1,500. Just keep your eyes open.