The price of laundry varies so much across hotels that it is hard to make generalisations, I've stayed at hotels where it was $15 USD for a t-shirt, and there doesn't seem to be any relationship between the hotel category and the price of laundry. I think the most expensive laundry I've encountered was in Busan, South Korea, where I spent over $200 USD just on a few days worth of clothes. So, by comparison, Courtyard Kuala Lumpur South is very cheap but it might be expensive for your needs.

Assuming you're also wearing women's t-shirts, the price here is just 8 MYR / $1.75 USD per t-shirt:


If you're travelling with a large group, I think hotel laundry is probably cost ineffective. The good news is, most places, especially in Asia, have third-party laundry pick-up and drop-off services that charge by weight or laundry bag rather than by item. I don't typically use them (because the price difference isn't too big on a small number of items) but they can be very cost effective for large volumes of laundry. I'd guess you can get a family of 5's laundry done for <100 MYR by a pick-up service. For the Courtyard Kuala Lumpur South specifically, there is also a few laundry services within 2 minutes walking distance.