Here's just one thought on reducing the costs of solo travel. I know that hostels and other alternative accommodations can be had when travelling. Hey, even camping is a possible alternative if you are prepared for certain locations.
My suggestion for those who don't want to rough it, but would like to "share" accomodations, is to shop around online for a "buddy" who also wants to solo travel to the same destination as yourself.
This "shopping for a buddy" would have to be very careful, but it can lend itself to making new friends on your journeys. You could probably go "buddy shopping" much like you would use an online dating service, or other online ad services. I would however recommend a good deal of judgement in choosing your buddy before finalizing anything. You might want to list your wants, needs, do's and don'ts so the potential buddy is aware of your leaning(s).
The reason I suggest this: it comes from my years of "solo" SCUBA diving travel, where I would meet divers and then have to buddy up with someone. Usually, I would be very fortunate in my pairing or selection. However, I could tell stories of those who were not the best bud.
I still think the idea of "buddy" travel falls under the purview of solo travel, as it not only allows each solo traveller to pair up with another - in some cases a number of solo travellers or pairs end up forming groups - but it also allows each solo traveller to choose to do their own thing if they so choose. The buddies do not have to share meals if they don't want. They don't have to share tours or exploring. It is kind of nice though at the end of day though to sit down to a drink with someone who shares your language and similar travel objectives and chat it up about what each of you have done. I have always found this fun in my previous solo travels.