From what I remember (and few sources can help to confirm, since, during the pre-patch of TBC the max gold a single character level 60 could carry on a realm transfer was 5.000G (up from 2.000G) and the level 70 character was 10.000G.
If the numbers back from Patch 2.4.3 will be used then it should look like the following:
Level 10-30: 300g
Level 31-50: 1,000g
Level 51-69: 5,000g
Level 70: 10,000g
So, during the pre-patch if transfers are allowed, you can carry 5,000g to another realm with you in case you are willing to transfer.
edit: values adjusted to reflect the real numbers back then.