Are you after tropical or coldwater fish?
And what size tank would you be looking for?
I have tropical fish, a 60 Litre fish tank cost me £90.
That included a filter, the filter foam, heater etc.
If you really are interested in fish keeping, you have to think about all the extras you will need on top, plants, gravel, ornaments, treatment incase your fish get sick, water tests etc.
If you do manage to get a fish tank for free, you will still have to pay quite a bit for all these other things in order to keep your fish alive and healthy! Though if someone is giving it away with fish, you might already get them with it. My auntie managed to pay £30 for a tank, including fish, so you might have to pay a small price. You could look in your local newspapers etc for a cheap tank.
And probably stating the obvious, you will have to clean your tank out often and do water changes. I've just cleaned mine out and it took me ages lol.
If you have any more questions feel free to ask and there are other people on here who are more experienced than me lol, but I am willing to give you advice etc.
But good luck finding one

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