If its a small farm, i would use dedicated proxies - vary from $1.50 to $3.50 depending on where you go. The amount of acc's you use per proxy is up to you. Some people use 1 acc per proxy and others 10 as they dont believe chain bans exist as jagex dont look at IP on first detection. i would try it out yourself. First proxy have one acc, second proxy use 3accs and dump the rest of the accounts on the third proxy and see if there is a difference with ban rates.
Good luck