Many guidebooks (including Lonely Planet Borneo Aug 2019 edition) and websites still claim that you can take Bus No. 6 (4 ringgit) from Kuching to Semenggoh.
However, my hostel staff tell me that that bus went out of service maybe 2 years ago. (Indeed, someone updated the Kuching Wikitravel page, stating "Attention: As of December 2018, there is no bus No. K6 at 13.00 anymore!!!")
They tell me the only ways to get there now are by taxi/Grab/tour arrangement, which seem to cost something like 90 ringgit for the return trip.
Are there any other cheaper ways to get from Kuching to Semenggoh?