voltage and current sensing isn’t a big deal. you can use bridge rectifier and voltage divider ckt to get TTL level voltage which can be directly fed to arduino analog pin. for high voltage isolation use small signal transformer or step down transformer.
for current sensing use CT(current transformer ), it provides voltage proportional to current flow. again with rectifier and voltage divider you can sense the voltage and convert that to current.
for internet link there are multiple options.
GSM/GPRS module, WI-FI module, LAN module.
anyone of them can serve your purpose. wi-fi and lan are highly reliable, GSM/GPRS depends upon cellular networks.
i can calculate the exact cost as prices may differ in particular countries but estimate will be around maximum $50 in india.
and be careful with high mains voltage.