Volks will have some of their basic Super Dollfies for sale in their showrooms, different showrooms will have different stock levels so you would have to visit a few of them to get a good idea of what is available. Try the showrooms in Akihabara, Harajuku and Shinjuku. Soom has a shop in Harajuku but they only display dolls you purchase from their on-line shop there, none are for sale.
If you want a Volks brand resin Super Dollfie it's about $360 for a 43cm doll and about $640 -$750 for one of the 60cm dolls. They do come with painted faces, eyes, wigs and a clothing set. If you want one of their Dollfie Dreams which are made of vinyl you'll spend about $200 for a 43cm doll and about $250 for a 60cm, but they do not come painted.
You can find second hand dolls at Mandarake and Closet Child, still mostly Volks but also some Blue Fairy dolls and Obitsu.
Many popular brands cost about the same as Volks dolls but there are cheaper ones to be found. You may want to join a forum dedicated to Asian Ball Jointed Dolls (like Den of Angels) and do more research before you decide what you want. Most BJD collectors buy dolls on-line, it's pretty standard. I don't consider it an Otaku hobby because (at least in the US) doll collectors come from many backgrounds and approach their hobby in different ways. There are some otaku who collect dolls but very few doll collectors are truly otaku.
I hope that helps.
