The passage in the Torah that is the source for people joining together into groups in order to bring the korban Pesah says that if a house is too small for an animal, he should take it together with his neighbor, according to the number of people in each family (see Shmot 12:4). This pasuk is understood by our Gemara to teach other halakhot, as well.
As it was taught in a: The verse states: “And if the household be too little for a lamb, then shall he and his neighbor next to his house take one” (Exodus 12:4). The phrase “if the household be too little” is taken to mean the household cannot afford the basic necessities of the Festival. Continuing this interpretation, the phrase “for a lamb [miheyot miseh]” is then taken to mean: sustain him [hahayeihu] from the lamb, i.e., he may use the Paschal lamb as a means of supporting himself. He takes money from his neighbor in return for registering his neighbor for a portion of his Paschal lamb and then uses that money to purchase his needs. However, this applies only if one lacks sufficient means to purchase food to eat, but not if he lacks only sufficient means to purchase other items.
Rabbi Yehuda HaNasi [Rabbi] says: It applies even if one lacks sufficient means to purchase other necessary items, for if he does not have sufficient funds he may register another person with him for his Paschal lamb and for his Festival peace-offering. And the money in his hand that he receives for registering that person is non-sacred, for it is on this condition that the Jewish people consecrate their Paschal lambs.
The discussion in the Gemara is: what else is considered an inherent part of the sacrifice that the money can go toward it?
Will the purchase of wood for roasting the sacrifice be appropriate use of the korban Pesah money? In this case, everyone agrees that the korban Pesah needs to be roasted and that the wood is an integral part of the sacrifice.
Will the purchase of matza and maror be permitted with this money? According to one opinion, the passage (Shmot 12:8) which connects the eating of the sacrifice with matza and maror proves that they are considered as one, and can therefore be purchased with money that was set aside for the korban Pesah.
How about the purchase of clothing that would be appropriate for the holiday? In this case the Hakhamim argue that clothing is totally separate from the korban and cannot be purchased. Rabbi, however, points to the expression mi-heyot miseh (see Shmot 12:4), which, relying on a switch of pronunciation from a letter heh to a het, he understands to mean that a person is permitted to support himself, to give himself life from the korban, and even for this use it would be permitted.