Depending on you're 1ph or 3ph supply, and how many amps. Take a pix and post lah.

I use 3 phase at home. The pricing of the device also depend on rated current. Hence if you're talking about single phase RCD, e.g. from ABB.os its 77 for 40A 30mA and 127 for 63A 30mA materials only

Wah landed!
I stay in highrise.
Long time ago supply only 40A per phase due to wire size small. So not very useful, hence prev owner put in 3ph so can use up to 120A.

U supply the parts yourself will be cheaper than asking the electrician to buy for you..But to get the right part w/o pic of ur existing is hard..err on the side of 63A 30mA 2P RCD. then get an electrician or wireman to wire it up should cost around there. For plug and play replacement you can shop around FB..some are pretty cheap on labour. My usual sub con costs from 200 to show up.