Was at Bromo last month, public transport all the way. Train (2hr) Surabaya to Probolinggo 50k IDR pax, Van (1hr) Probolinggo to Ceromo Lawang (25k IDR) pax, accommodation 150k IDR per room, jeep for sunrise 100k IDR pax or 400k-450k IDR per jeep (can take 5 quite comfortably or squeeze 6, but I think still expensive).
Met 2 Malaysians who share the same van with us. At Probolinggo, they paid 650k IDR pax (bargain down from 950k -> 750k -> 650k IDR) for package from Probolinggo->Bromo->Ijen->Surabaya. Price include transport (Probolinggo to Cemoro Lawang) + accommodation (Cemoro Lawang) + Sunrise jeep tour + transport (Cemoro Lawang to Probolinggo) + transport (Probolinggo to Ijen) + accommodation (Ijen) + transport (Ijen to either Surabaya/Gilimanuk).
Met another European couple who paid 900k IDR 3D2N same trip but in-out of Yogyakarta.
If you came out of Probolinggo train station there will be many touts who will not sell you tour package but offer 3k IDR Bemo ride to bus terminal. The Bemo will drop you outside some cheapskate looking tour agencies (instead of terminal) where people usually booked their tours from.
If not in Jul-Aug, Dec (months where Australian/Europeans arrived) and not weekend, there is no need to book rooms online. You get much better rates and can view/choose rooms/guesthouses onsite. We got a room listed as 180k IDR on brochure/online, was offered 150k IDR but bargain down to 120k IDR each room for 2 rooms.