That's a pretty cheap price for Antminer s19 pro if you can get it for $6,350 each. Just make sure that you are dealing with a trusted distributor or seller.
About the ROI it will still depend on the Bitcoin price and difficulty since the difficulty drops well it still worth having those gear and hold your mine coins for the next block halving.
According to some tools, the ROI is 2 months and 15 days to reach the ROI you can check for yourself and use this tool below
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https://www.mycryptobuddy.com/BitcoinMiningCalculatorJust include the hardware cost in total and the power consumption including the total hash rate.
I’m actually buying them brand new, from a chinese friend who has a chinese vendor in China, I know my friend in real life, and he is certain the vendor is trustworthy because he is his real life friend in China. They are all brand new units.
I will calculate the ROI and check, I’m not sure how you came up with only 2 months and 15 days, are you sure this is accurate? each miner makes aprox 30$ after electricy, so 10 of them would be making 300$ a day, which is 9000$ a month, the investment is 63500$, 63500$/9000$ is about 7-8 months, can you explain the 2 months and 15 days?