If you cannot afford a tank even a container that holds more water is better than a 1 gallon would be preferable. I have even used a bucket before for a tank as long as it is a new one. They can be heated and filtered and it just takes a sponge filter which is not expensive or a small filter designed for a small tank. (like the Azoo Palm Filter which is wonderful and inexpensive) and a 25 watt heater. It is not the best arrangement and could be improved on. I have seen large Tupperware like containers or Kritter Keepers like Hamsters or Small animals other than fish are kept in used. I have seen storage bins used. Any container that is water tight and can have a heater and filter used on it is acceptable. It would need to be at least 2.5 gallons or 10 quarts in size. In my opinion the Tupperware type of containers would at least let the fish have some light if you cannot get a small hamster or creature type of container. The bucket can be used but would be uncovered and would have to have a cover fashioned of some type of plastic canvas or something so the fish could not jump out or the water level would have to be kept low enough for them not to be able to come anywhere near the top. This would mean a sponge filter for sure as a
HOB filter would not reach deep enough to do a good job.
My suggestion to you would be:
A small Tupperware container
A small Sponge Filter
Airpump
Airline
25 watt heater
If you went to Walmart or a Dollar Store the cost of the supplies would be considerably less. The Dollar Store would probably have a big enough container for you for $3 or less and Walmart would have the small airpump and filter set for less than $10 and the heater for $10 or so and the airline for about $2. Now I was a student once and you can use the money all the time I know. This is $25 and I know that money does not grow on trees but It is the absolute cheapest way to go unless you happen to have a Salvation Army or Goodwill store about that may just happen to have what you need there and some times using used heaters and pumps and all is risky. They tend to fail when we least want or need them to. If you were not a student, I would not even consider the Walmart heater. I would be saying to you do not skimp on the cost of a heater and insist on the best as the best is only a few dollars more and is guaranteed for life. It is the Visi-therm Stealth heater by Marineland and they put them together to last because they guarantee them for life and do not want to have to replace them for free. They also hold the heat even and do not give you a surprise in the middle of the night some night. But they are usually around $18 and then you cannot always find them locally and have to order them and that means postage. I have no idea where you are and what stores you have around you but unless you have some regular pet stores the resources may be limited. But everyone has access to somewhere to get a square box of plastic and a small heater of some kind even if they cannot get a filter and have to continue to do the water changes daily. If you have a 3 gallon container a 1/3 water change a day (1 gallon a day) would be enough until you could afford to get a small filter and get it cycled. Cycling with fish does take time though so be prepared for 4 to 6 weeks after you install the filter.
Rose
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Okay, I'll change the water less now, thanks for the advice, and I'll be on the lookout for a bigger tank.