Approximate wealth in Magical Items and the like your domain could start with can be found in the list below.
To find the right amount for your domain, take your regents total character level, and if he either have a Major or Great Bloodline, add one or two respectively.
Magic items is then bought according to standard market price as listed in the DMG and/or SRD.
No magic item not listed in those places can be asked for in start of play. Non-standard items will only be introduced by the GMs.

1st 900 gp
2nd 2,000 gp
3rd 2,500 gp
4th 3,300 gp
5th 4,300 gp
6th 5,600 gp
7th 7,200 gp
8th 9,400 gp
9th 12,000 gp
10th 16,000 gp
11th 21,000 gp
12th 27,000 gp
13th 35,000 gp
14th 45,000 gp
15th 59,000 gp
16th 77,000 gp
17th 100,000 gp
18th 130,000 gp
19th 170,000 gp
20th 220,000 gp