With the MKS/OKS and EPL mods (or just EPL alone), it's possible to build rockets in orbit instead of launching them from KSC on Kerbin. Or you can build on the surface of a different world.
Approximate cost to LKO (90km orbit above Kerbin's surface) for 9600 RocketParts is about 105k funds or about 10.9 funds/part. I'm using the StageRecovery mod to recover the boosters, otherwise you'd have to use a spaceplane to get costs that low. It's possible that I could drive costs lower by launching even more RocketParts in a single launch (maybe 10/part).
You also have to ship up any consumable supplies, like rocket fuel, RCS fuel, life support as they are not included in the EPL construction process.
Another requirement is that you need engineer kerbals with at least 2 stars of experience. Preferably with only low-medium stupidity levels. Plus life support if you use TAC-LS.
A single RocketPart weighs 2.5kg and costs 5 funds.
Update #1: Tested out a 495k gross funds launch vehicle, capable of putting 28.8k of RocketParts into LKO (17.2 funds/part). That should be about 144k cost for the raw RocketParts with the rest of the cost for the booster and infrastructure. StageRecovery results in about a 225k refund for a net launch cost of 270k or about 9.375 funds/RocketPart.