So long as it's not cracking inside the tire, and cracking is only superficial (not deep) then there is hardly any risk in running that tire, so long as you are running them at correct tire pressures and aren't abusing them with aggressive driving habits.
Should you take that risk? That's for whoever is reading this to decide. I will run tires until I see that the cracks are too deep, which is what actually happened last year.
As for buying older tires with good tread on them for cheap, they could very well be perfectly fine. However, if they are 7 years or older, I'll pass.
I'd rather pay extra for better tires, but that's mostly because I demand more from them around the turns than your average driver. For the average driver, assuming you can see how deep the cracks and regularly check your tire pressures, it's no problem. Tires are incredibly durable and resilient.