Once the basic mechanism is worked out,
(1) It should matter on equality of the spouses, based on current titles and so forth. I don't like shelling out money (currency was rare, I know it is probably meant to represent stored resources) When a dynastic union is a possibility, both parties should hold the same tier of titles; historically, Fernando of Aragon was made king of Sicily by his father so that he would be equal to Queen Isabel of Castilla, just like Carlos V made the future Felipe II "king of Chile" when seeking the hand of Mary I Tudor. Even then, some diplomatic concessions (such as land, maybe adjustments to succession laws, etc.) should be sought out.
(2) unequal marriages as they were termed should cost a lot more; here prestige should come into play as well as the negative reaction of your own vassals. (weighed somehow on local norms if that is possible) In such cases, you could just pay money to even things out.
1 Just to nitpick, but Karel V made Filips II king of 'Naples' (Sicily) not Chile
2 I like the idea, but it should also depend on the position in the line of succession; this reaction should be less for younger children of the monarch.
Furthermore a count with connections with the higher nobility, maybe a distant descendant of a monarch, should result in less objections, than a nobody, who just was created a count.