Check out this document developed by META:
Guide to the Principal Archaeological Sites of
the Eastern Pamirs.
Robert Middleton, who developed the pamirs.org site, has also co-authored a book on Tajikistan and the Pamirs, which is an excellent addition to his site.
The challenge you face is what faces many travelers to this very, very remote and very little traveled corner of the world. The tourism infrastructure is still quite basic. Central Asia is remote. Tajikistan is remote for Central Asia. Gorno-Badakhshan is remote for Central Asia. Murghab is remote for Gorno-Badakhshan. And beyond Murghab, it's just you and the yaks pretty much.
None of the sights I saw in the area, except one tiny museum and an old fort that was, in any case, right by the side of the road, had any signage whatsoever, much less any local guide or brochure or other information. And none of the homestays have signs either -- although you should get homestay names from an NGO in Khorog, and if you stop somewhere unexpected, your driver will likely know someone who takes in visitors.
The drivers you would hire in the area would know some of the tourism places you would want to visit, but even they haven't likely visited all the sites. But you will want to do your research in advance and decide what sites would be of interest to you to visit. (Very few folks outside of Khorog and the META folks in Murghab speak any English.)
Another note about "the cheapest place to find a driver." Tajikistan is the poorest country in the very poor region of Central Asia. Most families have at least one if not more family members living abroad to work to send money to their families. One of the few ways that folks can remain in the area is by developing tourism as a profession and a way to develop community-based tourism. You may be a "budget traveler," but the very fact that you have the time and the money to travel internationally makes you extremely wealthy compared to the folks here.
This is a large and remote and inhospitable region. The few people that can afford a car and get the training to be able to repair it on the side of a mountain with baling wire and chewing gum and can afford to order parts that are crazy expensive to ship here and to know where all these odd places are that the tourists want to visit and to know the back-alley folks who can hook you up with a few liters of gas when the gas stations are out -- these "drivers" are much more than drivers and are a treasure for travelers.
On the main legs, sure, a shared taxi is the way to go, and that's how I traveled from Khorog to Murghab, for example, and I would recommend it for the leg from Dushanbe to Khorog if you can't take that most beautiful flight in the world. But for sightseeing, I would highly recommend digging into your budget and organizing a trip -- such as through the Wakhan Corridor to Langyar, stopping for the sights along the way -- with a driver from a community-based eco-tourism organization like Pamir Highway Adventure (formerly META), an organization that is striving to support folks in the local communities rather than private travel agencies in Dushanbe -- and support tourists by providing good training to the drivers about how to cope with the cultural and language issues. They are worth the very high price you will likely pay, for all the reasons discussed above, so please do not complain. Of course, you are always welcome to hitchhike, too.
Contacting Pamir Highway Travel is the best way I know to find the current prices, if you haven't found any info by doing an Advanced Search here at the ThornTree. There is usually a per-kilometer fee, plus a daily rate for the driver.
Also, if you take a one-way trip, especially in the off-season such as April, you will pay for both ways, per kilometer, because the driver has to go both ways and likely can't get a passenger for the return trip. I took a somewhat circular trip for my sightseeing, going out from Khorog to Langyar via the Wakhan Corridor and returning to Khorog via the Shokdarya Valley. Then I took a shared taxi from Khorog to Murghab. Then I took a META jeep from Murghab to Sary-Tash in Kyrgyzstan.
