BE ERCHECHA NAPHSHOT: It is not immediately clear what this means, nor how the translation is obtained from the given Yehudit. A "personal vow" perhaps? Most English-language translators regard it as a "special vow", by which a person is dedicated to YHVH; but what do either of those terms mean - the latter would surely be a vow of Nazirut if that interpretation were correct? Rashi (who lived from 1040-1105 CE) comments: "to give the valuation of his life, i.e., saying: 'I take it upon myself [to donate to the Holy Temple] the value (בְּעֶרְכְּךָ) of a vital (נְפָשֹׁת) organ" - by which orthodox commentators assume he means the head or the liver, though it is not clear how one would have dedicated these body-parts in his day, or in Biblical times; and if it was not organ-donation in the medical sense, then what was it?
The source for his exegesis is given as Torath Kohanim 26:57; but Torath Kohanim is simply the alternate name used by Talmudic commentators for Va Yikra/Leviticus (see here/p2), so in fact his source is... Leviticus 26:57, only there is no Leviticus 26:57, because that chapter ends at verse 46. At least, it does in the versions we are using today, but the Masoretic text was not yet finalised in Rashi's day; nonetheless we can safely assume that his source was this chapter and that the named source was an error.
A second source is also given, Arachin 20a, and this is much more useful. As the text in the link explains - in a rather unorthodox English, translated, I suspect, from a much more orthodox Yiddish - "Leviticus 27 describes the laws regarding the dedications of people, animals, and houses to G-d. The dedication involved sacrificing the item in question to G-d. In some cases, such as in the dedication of animal, the item could be literally sacrificed. However, in other cases, such as a person, there is a general principle that the sacrifice was substituted for a monetary payment given towards the service of G-d... The Talmud (Arachin 20a) interprets the phrase בְּעֶרְכְּךָ נְפָשֹׁת to refer to vital organs of the body. Hence a man could dedicate his heart or liver to G-d. However, this was interpreted as meaning giving an amount corresponding to the value of his life. Again, as in the case of dedicating an unclean animal, we see that dedicating one's life meant in practice giving a certain compensation to the Temple treasury... To cross-validate what I have claimed above, consider the redemption of the first-born male child. Numbers 3:45-47 records G-d commanding Moses to take the Levites in place of the firstborn male children of Israel for service in the Tabernacle. Moses is also commanded to take five (silver) shekel coins for each of 237 people in excess of the Levites. The firstborn male children of Israel were originally supposed to serve as priests. But as Jewish tradition holds it, they forfeited this right to the Levites due to the sin with the Golden Calf in Exodus 32. As the firstborn males can no longer be holy to serve in the Temple, they must be redeemed for an appropriate value. And this practice actually continues to this day in Judaism."
So we can now offer a revised translation: