Using late 2013 iMac 21.5 inch as an external display for another computer

Hi

I will soon be buying a mid-range late 2013 21.5 inch iMac and I am wondering if there is any way that I can connect my Windows PC to it to do a few things that currently aren't available to do on the iMac. I will be using the iMac as my primary computer and the PC whenever I need to. I have a very small physical workspace so am unable to have more than one monitor. I have considered using boot camp on the iMac but even with a Windows partition, the graphics card in the iMac isn't powerful enough for what I need to do and it is the only thing that I find the iMac lacks in for my needs. Are there any hardware solutions to this problem, as software solutions that I have looked into are either too expensive or have too much latency, plus I need a physical display instead of a purely virtual one.

I have been researching this on the internet but have been confused by all the different responses so would be very grateful if you could help.

Thank you