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Yes, it is a bit expensive, and difficult to find gpu's for sale.
If you have an old desktop computer i would have tried it, maybe you can get something with the equipment you already have.
If you know the name of you card(s) you can easily check what you can make at https://www.nicehash.com/profitability-calculator

Got 3-4 old desktop computers around here somewhere, but the hardware specs are so ancient that they are not listed on nicehash. And my guess is that they use way more electricity than the amount of revenue they can create.

If I had old hardware I would have put them into mining right away, for me electricity doesn't matter, because i believe that bitcoin will rise to enormous heights the next years. maybe you only make $0,5/day now, but when the BTC price goes up maybe you really made $10/day(or more?), if you dont sell your BTC now that is.
5years ago I bought a asic miner, but i only had it for 2months because of the electricity cost vs income was going down to zero. but if i had known that BTC would be $10000 today i would still have used that old asic miner. at the time when I was mining the price for BTC was under $100.

Checked the hardware a bit closer and what I have is older core2duo cpus, no gpu. Old things I got for free from a school when they upgraded their hardware. The one gpu I got is a older Geforce GT 610. Am I right in thinking that there is no point in setting those up for mining?

I think you are right.
But it only take 5-10min to set it up using nicehash to see if it does hash.
go to nicehash.com, make a user. then download the software, let it run trough the benchmarking, and it will show you how much it will make. https://miner.nicehash.com
to make the most out of your cpu put it in Nitric acid, wait until it dissolves, pour the acid into a container and melt the gold in a furnace ;)

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