I've gone through a ton of AC routers that are cheap ever since I found Walmart clearing out the DLink 810L for $10-$20 last year. I've tried/played with the Linksys EA6200,EA6400,EA6500, Asus RT-AC56U, 1 Belkin, 1 Trendnet, and that Archer C7 that both smallnetbuilder and wirecutter recommended.
You will not find any of those for $50 at Walmart or BestBuy. What I recommend at the moment for cheap is the Linksys EA6200 at
woot for $28. It's AC566 but installing DD-WRT re-enables AC866. It's gigabit, 5 internal antennas. 3 of which you can change DIY.
However in your price range, nothing beats the ASUS RT-AC56U. I was sorely disappointed with that Archer C7. Newegg has it $80 with a rebate and I was pretty excited, but SORELY disappointed. It uses a very early gen AC chipset that doesn't even support beamforming. Apparently beamforming is what's required in my home for coverage. The end result is the ASUS and the Archer had the same signal strength at my two of my fringe locations.
The ASUS also DD-WRT compatible, but it doesn't need it. It's firmware is the best I have seen and feature RICH. You can dual failover your internet using another Ethernet or even plug in a 3G/4G LTE USB dongle for Internet. Newegg had it on sale for $50 4 months ago, but I have yet to see it at that price since.
Keep an eye on flash newegg, groupon (ya groupon!), and woot. Woot frequently has Linksys routers on sale. from that cheap EA6200 for $29 all the way to the monster WRT-1900AC at $139 and even the monsterous MIMO AC3200 for similar price. Though it's useless unless you have devices that support it.