xeromist is right, many people had the same dilemma. I had a headache trying to hook up an old 30" QXGA monitor which only has dual-link DVI, ended up using it for my second system with a compatible graphics card.
I haven't tried this cable personally, it appears to be one of very few worth investigating. It probably makes more sense to use that money to upgrade to a new monitor unless you can find one of these for cheap (albeit it needs another mini DP to DP adapter).
https://www.amazon.co.uk/Apple-MB571Z-Adaptor-DisplayPort-MacBook/dp/B001IF252C
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FPS, Racing, and VR Gamer / Tech Enthusiast / ROG Admin