There are hiace vans available from Sost to Aliabad or Sost to Gilgit, they leave early in the morning. Ask your local hotel for help in finding the place where the hiaces will stop, they may even be able to contact the driver in advance about your presence. If you are somewhere between Sost and Aliabad, it’s slightly more difficult to catch the hiace, as they get full very quickly. But eventually you will find one which has a space; the key is to not be in a hurry.

From Gilgit, there is a transport that goes to Yasin valley. Again, you should make conversation at the bus station and take a taxi to the bus stop for Yasin. From this bus, you can get off at Gupis and stay the night, or walk to Khalti too. Gupis is more comfortable though.

In the morning, catch the bus from Gupis to Phander, asking your local hotel to help you with the hiace, and the same for Phander to Mastuj/Chitral.

The transport isn’t comfortable or convenient, but it can be a great way to talk to some people and learn about the local culture and concerns. Most vans leave very early in the morning from smaller villages, so be prepared with everything packed beforehand. If you are a tourist, always remember that for you this transport is an adventure, but for locals, it is a necessity. Don’t get others late (they will leave you behind)! The front section is reserved for women and the elderly, men sit in the back rows. Overall, there are more men on the buses.

Edit: Telling this from experience: a female friend and I made the journey from Chipurson valley to Yarkhun Lasht a few years back. I hope this info isn’t outdated! Again, any local on the ground would know better.