How affordable?
I'm not too hot on monitors, but looking on Newegg they seem to start around $300, and that's with a slow (5ms) response time.
I think 1ms is better because there will be almost no blur around moving images, and in gaming, almost everything moves fast, so you probably want that.
I think this is best- http://www.newegg.com/Product/Product.aspx?Item=9SIA1N82837843&cm_re=4k_moniter-_-24-236-399-_-Product but iI'm not your best man for monitors, but this one has its own speakers, 4k, 60 Hz, and what I really looked at, a good brand name and good reviews.
Might want a second opinion on that though.