WiFi Boosters

hi guys wats up...? hey im researching on Wifi booster which i can use to communicate between me n my neighbours...i need a range of 500M 180degree....but the prob is the ranges on booster are given in dbi's so wats the conversion method....n any cost estimation? and will i have to buy special router for it? like i have a 108m Tp-link router ....will the antena be replaceable...do inform me n help me out in buying one....