Has been in business for many years, as it was founded in 1990. Supposedly has a very wide selection covering a variety of eras and topics.
1054 Bajcsy Zsilinszky u. 34
Phone: 061 / 311- 90-23
Monday - Friday 10-17:30
Founded in 1991. Apparently has a helpful staff.
1062 Budapest, Andrássy út 56th
Pesti Forrás Antikvárium
This shop appears to boast a special selection in history books and books about science. It has books that are more than a century old and also features old postcards and photographs.
1062 Budapest, Aradi utca 28.
Monday: 8-16. Tuesday - Wednesday: 12-18 Thursday: *12-20 * Friday: 12-18
Apparently well organized as well as carrying a wide variety of books.
1055 Budapest Szent István krt. 3
Phone: 06 1 / 311-6431
Monday - Friday: 10-18 Saturday: 9-13
Supposedly has "really helpful, youthful and helpful staff".
1053 Budapest, Museum Boulevard 39
Phone: +36 1266 -2653
Monday - Friday: 10-18. Saturday: 10-13
Attribution: I have mostly used a single source. I have never been to Budapest, and have no personal experience with these shops.