I got a Blyss 10L dehumidifier from B&Q. £100 odd.
3 bed flat (2 adults, 1 kid), all on one floor (converted house) so it wasn't designed to be chopped up and blocked up as it is, airflow not great (bathroom has no extractor fan for example, no airbricks of note, main house stairwell blocked up and doored off, etc)
We dry clothes inside year round (access to outside is a pain in the arse)
Dehumidifier required from mid-September to mid-March as we can't have the windows open as we can in summer as it just gets too cold
Generally have it on whenever anyone is home and we can move it into whichever room has washing in or has condensation on the windows (front windows double glazed, rear windows not all double glazed)
Never leave it on when not in (but one of us is generally in 5/7 days a week)
Don't leave it on at night (we could but just never have needed to)
Noise wouldn't be a problem if in a room with a closed door, without a closed door in between you can hear the general hum it but it doesn't bother me (and I work from home 2-3 days a week). Don't know what it's like for the downstairs neighbour but he's never said anything (and he would if it annoyed him)
Apr-Sep the sensor tells me it's roughly 50% relative humidity indoors and no condensation and no damp feeling in the air
When we start to feel we need to use it then it's usually reading ~60%
With a fresh load of washing drying it can go to over 70%
It occasionally looks at my slightly menacingly but has never killed me (yet)
If it's on for 12h then I'll have to empty the 2L collection tray thing twice a day, so it's performing close its rated capacity of 10L/day.
For running costs, I'd say it's on roughly half the time between September and March, so that's half of half a year. It's rated at taking 200W so on the basis that 1W per year = £1 (see cals below) that means it's costing us £50 a year, plus it kicks out a bit of warm air so part of that also reduces heating costs (although it won't be efficient).
It's certainly cheaper than buying/running a washer-dryer and is also sorts out the condensation that we'd inevitably get if we didn't ever dry clothes inside, something a washer-dryer couldn't do
- Electricity is roughly 12p per kWh. So 1W for an entire year = 8.76kWh. 8.76 * 0.12p = £1.05