https://www.walmart.com/ip/NETGEAR-RangeMax-WNR3500L-router-802-11b-g-n-draft-2-0-desktop/14663200
if someone had 4Mbs internet do they need to have a wirelss ac standard router or would any router work?
any will work
if you have gigabit any router will work too though
it really depends what you want from it.  like if you have a remote file server on your LAN then wireless AC would be nice even if you had 4 megabit internet
also some routers have better range than others, and you may want a single router that can cover a larger area, but that can still be hit and miss depending on the house etc
they will not be transfering files just for wifi
why not just use cellphone network at those speeds
but yeah unless heaps of interference you shouldn't even need 802.11n let alone 802.11ac
do not have a cellphone