When you find yourself in the situation where you just bought your second train, but you have no money to make a decent switch where trains can pass each other, think about using a depot as a switch.
1. Make an assumption where the trains will run into each other, and build a depot a little bit closer to the side where the empty train that just made a delivery will come in.
2. After making the depot send your empty train to the depot.
3. While your empty train is running towards the depot, make sure the second train doesn't crash into the first one. Manually stop the train if needed! (Tip: When you are sure that the trains will crash you can slow the second[full] train down manually to about half it's maximum speed. This way you still keep the train running and you aren't forced forced to stop the train totally).
4. After the second train passes the depot force your first train out again.
This is a viable option untill you have up to 4 trains running on a single track. After that it will be a mess and very hard to control. Once you can affort it, start double tracking.