I don't know if this was on the server at some point, but it might be good.
In the shop, i suggest that player have an option to buy exp.
For balancing this new feature, I would say 50k for 100 experience and can players can buy it once per match.
That means (with the maximum amount of 350k), the player can get 700 experience over 7 rounds (and ~900 per map IF they are willing to consume their money on experience only).
But, if you consider that this is not balanced in the favor of the player, you right, but there are situations where the player have the maximum amount of money that he can store and doesn't have a use for them, so, he can buy 100 exp. with 50k and still earn 50k by the end of the round (not wasting so much money).