Lazarus has a point here accomplishment should equal budgets! But the ever expanding budget makes for little realism and feels just to simple of a balance. Make the budget based on a simulated Public option like NASA today. Get a kerbin into orbit take a publicity photo get more budget. Use the achievements like those found in the mod of the same title to spike interest in your space program. Commit to a achievement or program (like Apollo, or Constellation) On the flip losing space craft or worse kerbals can dent budgets even ground projects/programs. Random events of space races, rescue, missions, challenges, war (not in space) or outreach campaigns to educate and stimulate interest http://mobile.geek.com/latest/252570-kerbal-space-program-gets-a-nasa-backed-asteroid-wranging-expansion would be incredibly immersive.