Solid State Drive for small commercial print shop
I would suggest a Samsung 850 PRO. Great longevity, warranty and performance. Or, if you want a bigger drive, get the 850 EVO. Not so durable, but we're still talking of decades. 

The Pro is rated for more writes than the Evo but costs more and has slightly higher benchmark performance. On an older iMac it’s not clear you’d benefit from the faster or more durable option.

Basically: 1000 write cycles per cell for the EVO and 3000 for the PRO. If you write 10GB/day (which is quite a lot) on a 256GB EVO, the disk will die in about 70 years, when you'll have written 256x1000 GB of data.