I am pretty sure our vent pipe is obstructed. I can't see what exactly it is (too far down, but must still be above where the upstairs toilet joins as that still flushes. I don't know if it is bird, squirrel, etc.)

Is there a safe way for me to remove the obstruction without great risk of pushing it down further?

I am not opposed to having a professional do the job but have no idea how much a typical plumber would charge. What would some of you plumbers charge (and what part of the country are you?) We are in Northeast Indiana, if anyone is close.

If hiring a professional is the way to go, I will make calls this week. But, I wanted to get an idea of the price/cost first.