$25K sounds about right, depending on where you live and how much sun exposure your roof gets (though there are ways around the latter). For 3kw 24/7 you need a 6+kwh system and a battery with enough juice to provide 3kw on average for roughly half the time. Those are top of the head estimates, you can use calculators found online to get more specifics, but in the extreme rough estimate range, if you are having a system professionally installed $25K seems about right for that load.

If you want to figure out installing one yourself, on the other hand? That can probably shave $5K off it, more if you can get the parts wholesale, but it does mean being confident working with household wiring and dealing with local codes and permits.