I have 2 rubbermaid and 2 freeland plastic/poly stock tanks ranging from 60 to 300 gallons (some are ponds, some to water the sheep). Bought them all at Fleet Farm (a feed-type store). The oldest is 9 years. None of them leak. Also have a 150 gallon galvanized it doesn't leak either, but it's new this spring. I paid about $110 for my 300ga tank.

Some people use plastic garbage cans, rubbermaid totes, or plastic kiddie wading pools (netted) to temporarily hold fish (depending on how big they are). All would need the right filtration, etc. Our Family Dollar Stores also sell plastic tubs the size of a 1/2 whiskey barrel (about 30ga) that might work for $6.

I bought my galvanized stock tanks that are 10ft wide and 1200 gallons at a local farm and ranch store.

They were about $250, which included the delivery fee.

They didn't leak.

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Stocktanks for livestock don't leak. The area around them in always muddy because the animals dribble water or play in it or overflow it.

I agree that what appeared to be leaks was probably other water from filling the tanks or something else. They generally do not leak. If they truly were leaking it was most likely around the drain plug which can be easily sealed. The tanks also might have been shipping damage ones they were using for display purposes.
I priced tanks here a couple of weeks ago. They are not cheap. Galvanized tanks are usually leass expensive than poly tanks but they also in time will leak due to pin holes,leaks around the seams, etc. These can be easily fixed. If you don't want to deal with that then you will need to buy poly tanks and unfortunately pay the price. Rubbermaid tanks will be more expensive than other brands of poly tanks so shop around.
Another option is you could place an ad in a classified paper that you want to buy used poly stock tanks in good condition. You might come up with some for a better price.

Have you tried craigslist?