I also go to Osaka in mid July for around 10 days for my family (couple with 3 and 7 yrs old kids). I used to book package through 歐陸旅運 (one office in Mongkok and one office in Wanchai) which I used for many years. They have a series of publications for 自由行.
My package is around HK$4380 for adult and HK$3880 for kids for 4 nights Osaka hotel and the freight is Cathay Pacific. I extend 2 nights in Osaka through the agent. I take care the booking in Kyoto by myself for other days.
I can also ask them for some of my queries for the trip. Of course, choosing their non-busy hrs for the questioning.
歐陸旅運 details are as follows:-
T: 2771 0982
F: 2782 4388
Address: Rm 1616-17, Hollywood Commercial Centre, 610 Nathan Road, Mongkok, Kowloon.
Office hrs: 10 am - 7 pm (Mon to Sat)
but close for lunch from 12:30 pm to 1:30 pm
One more point to remind you that $800 will be added to the package if you leave HK on or after 15/7. $500 will be added if your ticket extend to 14 days. The $$ for package quoted before is exclusive of these two items.
I cannot tell the agent is the cheapest. But at least their price is competitive.