Hi Stephan,
I got one recently for my 150mm refractor. This one:
https://www.ebay.com.au/itm/162211859887?ul_noapp=true
I can put it in with the finder and diagonal attached, and it is well made and well padded.
There are smaller ones here, for less than $20:
https://www.ebay.com.au/itm/60-70-80....c100005.m1851
They have free delivery too. Mine took about 2 weeks to arrive from China.
Lots cheaper than dedicated "telescope bags"!
All the best,
Dean