I have looked at the value of a GB and as many before me have
discovered I also found that a GB can not be equal to 2.000 gp.

If you look at what it cost for army units. The cost of the equipment
alone is much more worth than what you pay for it, even if you take in
to consideration that a regent might get it cheaper than regular
people.

For instance regular infantery with medium armor cost 2gb to muster.
If they have the following equipment, Hide Armor, Short Sword, Dagger
= 27gp. For 200 soldiers this ends at 5400. In this example the
cheapest of each equipment was chosen.
Well for 1.5gb you can upgrade these infantery to have heavy armor, so you sell the hide armor for 15 and buy a new splint mail for 200. This amount to 37.000gp or 24.666gp per gb.
These where just a few example choosing always the cheapest equipment in each category. I did several more where you could get as much as 80.000 gold for each GB.

I have made system to handle Finance, and would like to ask your opinion about it.

A gb is worth 5.000 x 1d10 gp. Each gb's value is calculated seperate even if
a bunch of GB if converted at the same time. When you have started a finance action you can NOT abort if you roll unfavorable on the d10.

So if I have 2 gb and want to use finance to transforme them in to gold i roll 2d10. First I get 1 and then I get 5, So I get 5.000 x 1 + 5.000 * 5 = 30.000 gp.
Then say I spend 10.000 and want to do another finance to converte
back in to the realms treasury. I rolle 1d10, gets 2. So my first gb
cost 10.000, then I roll again and get 10. So my next will cost
50.000, which I can not afford with my remaining 10.000 so I get 0.2 GB.
In the end I will have 1.2gb, had fun for 10.000 and spent two court actions on finance.

This system would to a larger degree work with the PHB values for
equipment, and it takes in to account that finace back and forth is a
unreliable thing to do. You can both make and lose large amounts of
money on it.

A addition requested by one of my players is that you are allowed to do a administrate (domain) check against DC 15 to modify the d10 roll by +/- 1, or DC 20 for +/- 2. You have to decide before rolling what target you are aiming at, if you fail you get no modification. So it is more risky to attempt to manipulate it with +/-2 han it is to attempt +/-1