1) The Pischei Teshuvah, printed on the page of the Shulchan Aruch (YD 157:4), cites the Pri Megadim who is in doubt about whether one must give up all one's money not to do a Lav d'Rabanan, but then the Pischei Teshuvah cites the Chavos Yair (#183) to whom it is obvious that one must give up all of one's money for this. The scenario of the Chavos Yair is someone being forced to drink Yayin Stam.

2) The Pischei Teshuvah also cites the Teshuvos ha'Radbaz (4:1216 (145, in our editions)) who writes that one is obligated to spend all of one's money to avoid doing an Isur d'Rabanan. This is because the Torah states, "You shall not depart from the word which they shall tell you, either to the right or the left" (Devarim 17:11), from which we learn that every Gezeirah d'Rabanan has a source in the Torah. Just as one must give all of one's money not to transgress a Mitzvah d'Oraisa, so one must give everything not to transgress a d'Rabanan.

3) Examples that the Radbaz gives where one must lose all one's money are in order not to drink the milk of Akum, or not to eat the fat of the sciatic nerve (Shuman of Gid ha'Nasheh).

4) The Radbaz writes that it is not only milk or fats but also "other Rabbinical prohibitions," so this seems to include everything that is included in the verse, "You shall not depart from the word which they shall tell you." However, I am not sure about the question of Chazarah or Hatmanah on Shabbos. The Shulchan Aruch (OC 253:2) writes that one may not put the pot back inside the oven. The Mishnah Berurah (#58) writes that since one returns the pot in the way that one always does on a weekday, it looks like one is cooking. This seems to be a prohibition of Mar'is ha'Ayin; it is forbidden only because it looks like something Asur even though it is not really Asur.

5) Now, we find a Halachah in the Rema (Shulchan Aruch OC 244:6) that if a Yisrael possesses the right to tax-collecting and he rents this right out to a Nochri for every Shabbos in the year, this is permitted and one need not worry that people will say that the Nochri is collecting the taxes for the Jew, because a financial loss is involved, and one is not concerned about such things in the case of loss. This suggests that in a case of Mar'is ha'Ayin, one is not always required to lose money. Possibly this might sometimes be a Heter in Chazarah/Hatmanah issues. This needs to be thought about more.

6) Here is the opinion of the Mahari Vayil cited by the Rema and Gra:

a) It should be pointed out that there is an opinion in the Rishonim that a person is not obligated to give up all his money in order not to do a Lav. This is the opinion of the Mahari Vayil, who was one of the Rishonim of Ashkenaz (he was a Talmid of the Maharil), frequently cited by the Rema in Shulchan Aruch.

b) The Mahari Vayil is cited by the Bi'ur ha'Gra (Shulchan Aruch YD 157:5) who writes that it appears from the words of the Mahari Vayil that for every Lav one is not obligated to spend one's money. The Mahari Vayil proved from the fact that the Torah states that one must love Hash-m "b'Chol Me'odecha" (Devarim 6:5) -- with all of one's money (see Mishnah, Berachos 54a), that this applies only to the prohibition of worshipping idols. The verse refers to the Mitzvah of loving Hash-m and tells us that one is required to spend all of one's money for this. This suggests that it is only to avoid Avodah Zarah that one must forfeit all of his money, but for other negative Mitzvos one does not. The G'ra concludes that the Mahari Vayil does not agree with the words of the Ran that a person is obligated to give up all of his money in order not to do a Lav.

c) The Aruch la'Ner (Sanhedrin 74a, DH b'Gemara l'Kach Ne'emar b'Kol Nafshecha) also writes that "b'Chol Me'odecha" applies only to Avodah Zarah, just as "b'Chol Nafshecha" refers only to Avodah Zarah. According to this, one would not be obligated to give up all of one's money not to do a Lav. The Aruch la'Ner writes that this is against the Shitah of the Ran cited by the Rema in Shulchan Orach (YD 157:1). In other words, the Aruch la'Ner was Mechaven to the Shitah of the Mahari Vayil even though he did not see it. (See also Marcheshes 1:43:13 in the name of Rav Chaim Ozer Grodzinski zt"l, who also asked the question of the Aruch la'Ner and did not have an answer.)

7) Here is the opinion of the Magen Avraham and the Gemara in Kesuvos 60a:

a) The Magen Avraham (end of Shulchan Aruch OC 307:7) writes that in a case of great financial loss, one may permit a Shevus, a Rabbinical prohibition, on Shabbos, to be done by a Nochri. Therefore, according to the Magen Avraham, one may ask a Nochri to perform Chazarah on Shabbos in order to avoid losing all of one's money. The Magen Avraham also writes that if a Jew does a Rabbinical prohibition in an unusual way (Shinuy), this is also permitted in a case of Hefsed Merubeh.

b) We also find in the Gemara in Kesuvos (60a, 6 lines from the bottom of the page) the idea that "b'Makom Peseida Lo Gazru Rabanan" -- where financial loss is involved, the Sages did not make a Gezeirah. The discussion there is about a pipe which flows down from the roof and has become blocked up by wild grass, with the result that the water spreads to the roof and drips into the house. The Gemara says that one may tread on the grass with one's foot on Shabbos, in private, and this way prevent the blockage. Even though one thereby mends the pipe, this sort of Tikun is permitted because it is done in an unusual way, so it is only forbidden mid'Rabanan. Since financial loss is involved, the Sages did not make a Gezeirah against doing this.

Kol Tuv,

Dovid Bloom