Sorry, is this a new build house? If so then these charges are normally made. Ours didn't cost that much but was over €500 and that was about 6 years ago and included the water supply and meter as well.
If it's a resale, unless your fusebox is really old then it shouldn't need changing. When I sold a flat the solicitor simply changed the name on the account online and didn't make any charge and there is no reason to change it simply because the account name is changing. If it does need a new fusebox because the old one is no longer fit for purpose then that still seems excessive. I paid £270 for a replacement one in UK including fitting so 900 euro does seem a bit much.
On the other hand, if there is no current contract (lapsed because of no one living there, for example, or a bank repossession) then the cost of connecting to the supply and fitting a meter is around €300. If the property is more than 20 years old then a "boletin" (safety certificate) would be required and these can cost upwards of €200 to obtain.
(When we first moved over, it would have been easier to keep the front door open and just throw money out the door at everyone who passed as everyone seemed to want something for this and something else for that. Expensive old business here).