Borrowing money and taking money from charity for the sake of the Shabbos meals:

Borrowing money to enhance Shabbos:[1] If one does not have money for Shabbos expenses he is to borrow money if he has an item which is able to be given as collateral to the lender[2].[3] Nonetheless, although collateral is needed, Chazal say that Hashem will arrange for him to be able to pay the lender back the money which he borrowed. This is consistent with the saying of the Sages that Shabbos expenses do not come out of one’s Heavenly ordained budget which is annually decreed on Rosh Hashana. If one does not own any collateral then he should not borrow the money in order to enhance Shabbos on the basis relying that G-d will reimburse him, as there is no obligation to spend for Shabbos more than one can afford.

Borrowing money with interest/Ribis:[4] It is permitted to borrow money under terms of Rabbinical interest[5] [Ribis Derabanan] for the purpose of enhancing the Shabbos and Yom Tov meal, as well as any Seudas Mitzvah. This however only applies if one is unable to borrow under a no interest rate.

Using money from a charity fund to enhance Shabbos: If one can afford two basic daily meals for every day of the week it is forbidden[6] to take money from a charity fund for the purpose of having food for the third Shabbos meal, or for the purpose of buying Shabbos delicacies.[7] However if one cannot afford two daily meals for every day of the week and is thus in need of receiving money from the charity fund for these two meals then he is to also be given money for the third Shabbos meal as well as for the Shabbos delicacies such as fish and vegetables.[8] Similarly if one already received money from the community charity fund he may use some of that money for enhancing Shabbos. However in such a case he must make sure that this will not cause him to need to ask for more money for his daily needs.[9] If one is unable to do so, then if he has some of his own money, he should push himself to use that money for honoring Shabbos to the best of his ability.

Asking for a present from a friend in order to enhance Shabbos:[10] There is no obligation for one to ask to be given money as a gift in order to enhance Shabbos as the Sages have stated “Make your Shabbos like a weekday and do not become needy unto the public”. One must budget himself properly so he is able to enhance Shabbos at least a minute amount. It is better for one to do so then to become needy onto the public [and ask for gifts to be able to enhance Shabbos].[11]

Proper budgeting-What is one to do if he does not have any extra money to enhance Shabbos and cannot borrow or take from the charity fund?[12] Even in a case where one has just enough money for daily meals and lacks money to enhance Shabbos, in which case he cannot receive from charity, nevertheless he is still obligated to budget himself during the week in a way that he will be able to enhance Shabbos a minute amount at the very least.[13] Likewise it is proper for him to have at least two dishes, as stated above.

Summary:

One may only borrow money in order to enhance Shabbos if he owns collateral which can be used to repay the loan. One may even borrow money under terms of Rabbinical interest if he is unable to borrow money on a interest free rate.

If one has two meals worth of food for Shabbos he may not take money from charity to buy extra delicacies for Shabbos or even in order to have food for the third meal. If however he does not have two meals of food for Shabbos he may take money from charity for all the Shabbos meals and delicacies. It is better that one budget his money during the week in a way that he will be able to afford the Shabbos foods rather than ask others for money as a gift for Shabbos expenses.