So I'm gonna take a holiday trip to Washington DC. Amtrak OMA-CHI costs an arm and a leg, so I'm driving to CHI. Is there any good place to park long-term (read cheap)? I can park at the airports and take transit to Union Station and back, if thats the best option. I'll be gone for 8 days, Ideally, I'd like to keep parking costs under 70$ for that time.