Tier 2 dependancy visa (for newborn child born in UK)

Hi
I am on a South African passport, and currently in possession of a valid UK Work Permit since Sept 2007, valid expiring Sept 2012. My wife and son already have UK Work Permit dependency visas in their South African passports. We have recently had a daughter, and would like to enquire how to obtain a dependency visa for her, which would allow travel outside of UK (and more importantly re-entry back to UK). I am hoping to apply from within the UK if possible, rather than having to fly back to SA (like we did for our son’s visa a few years ago).

Is this possible, what are the associated costs, how long does this process take etc? Any recommended Visa agencies? I have contacted a few already but their admin fees are ridiculous, @ £500 - £700 (not incl the UKBA fee of £550)

Thanks in advance
Darren

See also Dependent visa - non point based