When I started the company, we used the RPi as the WiFi Access Point. The trouble with them is that the built in WiFi module is pretty limited in its ability to handle many simultaneous users and to provide a robust signal throughout a space. You can buy 3rd party USB WiFi dongles, but I found that they have a high failure rate over their lifetime. i.e. not the most robust solution.
If you go the RPi route, you may find the following script helpful. This will bridge the 3rd party dongle to the local network, isolate devices from communicating to private network IPs, and forward HTTP/S traffic through the Squid HTTP proxy service. (sorry about the formatting):
#!/bin/bash
set -e
if [[ $EUID -ne 0 ]]; then
echo "This script must be run as root"
exit 1
fi
# Set the proxy interface based on the presence of wlan0 or not
if [ -e "/sys/class/net/wlan0/operstate" ] ; then
PROXY_INTERFACE=wlan0
else
PROXY_INTERFACE=eth0
fi
PROXY_HTTP=3128
PROXY_HTTPS=3129
PROXY_NETWORK=`ip address show $PROXY_INTERFACE | grep 'inet .* brd ' | head -1 | sed -e 's/inet \(.\) brd.$/\1/' | sed -e 's/ //g'`
# Allow traffic to the proxy's network
iptables -A FORWARD -d ${PROXY_NETWORK} -j ACCEPT
# Drop traffic forwarded to all other class A, B, and C private networks
iptables -A FORWARD -m iprange --dst-range 10.0.0.0-10.255.255.255 -j REJECT
iptables -A FORWARD -m iprange --dst-range 172.16.0.0-172.31.255.255 -j REJECT
iptables -A FORWARD -m iprange --dst-range 192.168.0.0-192.168.255.255 -j REJECT
# WiFi AP Only; Bridge WLAN to eth0
if [ $PROXY_INTERFACE = "wlan0" ]; then
iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
iptables -A FORWARD -i eth0 -o $PROXY_INTERFACE -m state --state RELATED,ESTABLISHED -j ACCEPT
iptables -A FORWARD -i $PROXY_INTERFACE -o eth0 -j ACCEPT
fi
# Let local Squid get out to HTTP/S
iptables -t nat -A PREROUTING -s localhost -p tcp --dport 80 -j ACCEPT
iptables -t nat -A PREROUTING -s localhost -p tcp --dport 443 -j ACCEPT
# Forward all HTTP/S to Squid
iptables -t nat -A PREROUTING -p tcp --dport 80 -j REDIRECT --to-port $PROXY_HTTP
iptables -t nat -A PREROUTING -p tcp --dport 443 -j REDIRECT --to-port $PROXY_HTTPS
# drop direct connections to the squid proxy
iptables -t mangle -A PREROUTING -p tcp --dport $PROXY_HTTP -j DROP
iptables -t mangle -A PREROUTING -p tcp --dport $PROXY_HTTPS -j DROP