I was at level 650 but needed 700 for the better Halloween loco. Along came B-day Bill and I made it easily. I finished off the first 51 Bill contracts and ended up at level 916, a bump of 266 levels. With that Vampiric Nobility 5 (Grand Steam) @185M coins per hour, plus Bill's Superb loco delivering 1.8M cargo per hour; my choice of 12 types of material to choose from, it adds interest to the game.
More than half the level-up came from coins. I sent some to International (bought high-cost decorations) and some came from local, including buying/selling the same high-cost loco several times. I think I spent 300B to 400B coins over that time.