We found ourselves in the same boat. Whilst the Avantext system is good to use and it's nice to have everything there (maintenance and parts manuals, SBs etc) it isn't cheap and will force Subpart F & G companies to specialise in types like manufacturer franchised car garages.
We look after 25 Pipers or so so the cost of the Avantext system can be split between them. Mooney SBs are available free on line, all Diamond info is available likewise. The cost of Cessna and Socata manuals are ridiculous - even Cessna through Avantext is far more expensive than the Piper stuff. Then there's the CDs for Lycoming and Continental...
If a 'rare to us' type comes to us then the owner purchases the data which we look after whilst the aircraft is under contract to us. If the owner moved away or the aircraft sold, the manuals go with the aircraft/owner.
I was told by my surveyor that the Subpart G part of the organisation must have up to dat data for the aircraft in manages at all times - no sharing between companies. Subpart F must have the appropriate current data when actually working on the aircraft.
As far as the approvals go how come a company at Sturgate got: 'Cirrus single & twin piston engine series below 2730kg' on their Subpart G. Anyone else got the manuals for a Cirrus Twin. Or even a picture of one...?!
Good old EASA!