Hi
I don't know what your interests are, or what level of "comfort" you're looking forward on a holiday, so it's hard to comment. Also how much you are willing to sort out yourself, or pay to have it sorted out for you
Having said that, there are a number of holidays types that do attract a high percentage of singles (although, mostly, they are not run as singles only). Although JY is a singles holiday, if you look back at previous threads you'll see there is a lot of discussion about people who know each other, or are related, coming on JY holidays.
Typical of these other holidays are walking holidays, and "adventure" type holidays. I suspect many of these holidays will be cheaper in total (including your own expenditure while on the holiday, and even with a single supplement), partly because they use lower grade hotels than JY, and also because they include more meals than JY in the price.
If you are willing to room share they become much cheaper, as single occupancy of a room is an expensive part of any holiday
In my experience JY offer a more complete package, for which you pay, of course, but are less flexible than other companies on things like "land only" prices, use of non London airports etc.
Solos are fine, they do age band some (but not all) of their holidays, and include less excursions than JY, but overall I suspect they may be cheaper.
Once you decide what kind of holiday you want, I would suggest you have a good look around at what's on offer, see what type of hotels they use, how many meals are paid for, what activities/excursions are included etc and go from there.
Stuart