My trip to Hong Kong will include 2 visits to Shenzhen. Please advise.

Hiya. Next January (2013), whilst on my journey to Manila, i am flying into hong Kong for a 6 day stop over... With prices of hotels very high in Hong Kong, i am considering booking my Hotel stay in Shenzhen... But still wish to visit Hong Kong on more than one occasion. If there is no reason to stop this idea? Which visa would i require? A double entry would allow me the first visit to Shenzhen and access to my hotel, with the second entry to China, a few days later when i return from a day trip to Hong kong.. Does this all seem feasible?
Other than the visa price, of £45 for the double entry, does the processing cost still apply if i am collecting visa from London/Chinese Embassy...?
Thanks in advance for your reply