I paid 6k for my shamrock 9 years ago....Took half a summer to get it ocean ready since the guy who owned it died while rebuilding it!
Be careful with older boats.....Aluminum tanks last between 10 and 20 years and usually fail right between there. The shamrock had two 20 gallong alum tanks, one on each side and mine leaked and oh what a bitch to get em out since they were foamed in.
Tell Grump Sams if he dont call me soon im gonna come lookin for him....
Those 20' Shamrocks go for the tune of around 40 sumptin K new I believe....They are not cheap boats.....There is a dealership in Harwich if you want to go look at them....