All components within hours for a public CofA.
All owner-signed-for maintenance re-checked and signed off by LAME.
All paperwork, particularly component forms 1 re-checked to be at Public CofA standard.
All ANs and ADs for public CofA use up to date.
The cost will depend a great deal on the type, ADs in force, how good the paperwork is, how long since it was operated on a public, and a small element of luck.
Might be worth checking how the EASA regs will change things, since I believe that it's moving to only a single category of CofA which may simplify things hugely. I'm afraid I've no detailed informaiton on that, your local CAA regional office might be able to advise.
G