I like the concept. Would want to simplify it a little. No extra action, simply list the statues in existence somewhere in the region details.
Would it work if there were a tab named "monuments" after "religion" that would show up only when there is at least one monument present? Clicking it would then list the monuments, the oldest one at the top. Alternatively you could list the monuments right under the region description, but that would perhaps force them too much on the players. It would give you at least some sense of visiting it if you had to click it to "go there".
Did you have a number in mind?
Actually, I did not. Some number like 500 gold might cut it, if they are to be seen as exceptional craftsmanship with rare and valuable materials spent. It has to be a high enough number to prevent them popping up left and right, and to also give the target character a feeling that someone has made a real sacrifice for his benefit, which is likely way out of proportion of the actual gain. It creates a nice bind there. The poorer you are the more so.
It should perhaps be seen as a vanity item more than a stat booster. A high price would also ensure that the realm would not look kindly if statues are erected here and there for silly reasons. It's gold away from the troops.
