Rashi on Leviticus 27:3/רש"י על ויקרא כ״ז:ג׳

1והיה ערכך THEN THY ערכך SHALL BE etc. — This word ערך used throughout this section has not the meaning of דמים, market-value (which varies according to the condition of the market or the condition of the person offered for sale, whilst ערך is a fixed value), but whether he be of high value or of low value, according to his age is the ערך fixed for him in this section.

2ערכך is the same as ערך (i. e. the second כ''ף is not the suffix of the second person masc. sing.). I do not know what grammatical form the doubling of the כ''ף represents.