Hi Denise,
The 15 pounds rosie refers to will give you unlimited access to Scotlands People for a full day 9.30 till 4 (I think) on one of the computers in the search room at the Mitchell Library. My advice would be to book your place in advance to avoid arriving and finding the positions all taken
If the system operates the same as the Burns Monument Centre in Kilmarnock - another location with computer access to Scotlands People you can purchase photo-copies of any certificates or census pages for 50p a copy, or you can take a flashdrive/memory stick and save them to that for no extra charge. Take a packed lunch (there will be an area away from the computers to take a break) and have the whole day there to get your money's worth.
As for the records for Carnegie Park Orphanage , I've no idea I'm afraid if records exist but if they do you won't find them on Scotlands People. The records could however be at the Mitchell which has other archives. Here is their website -
http://www.glasgowlife.org.uk/libraries/the-mitchell-library/Pages/home.aspx.
I would suggest you email the Mitchell and ask if they have records relating to the orphanage. Even if they don't they might know where they are.
Good luck with your research when you get here.
Looby