Not-so-high-speed rail advice

When we flew to Maine a couple years ago, we stayed at a Residence Inn in Eagan the night before we left, ($99) and they let us leave our car there for a week. They also had a free airport shuttle. That's not really close to Amtrack, but you might ask a hotel if they'd make a deal with you.

Could you board in St. Cloud?  Might be better long-term parking available there, as I think the train station is closer to city center.

Are there any one-way car rental options with drop off at the Amtrak?

There's also a lot near the airport you can leave your car at we've used -- they'll shuttle you to the airport, but I don't know if they will shuttle you to Amtrak station. Maybe you could call Amtrak station in St Paul and ask them if they have any long-term parking facilities nearby?  Or see if you can make a deal with the Kelly Inn -- they're a short walk from the Amtrak station.

Oh, you did talk to the station already. I'd call St. Paul hotels then or any downtown parking facility and see if you can make a deal with them. Then you could just cab it to Amtrak, it's like a $5 cab ride. Or call Xcel Centre, they might have long term parking facilities. There has to be something in downtown St Paul! After all, Skyline has a deal with the DECC for long term parking.

If you use Team Parking in St. Paul, which is the long term facility we've used, it's pretty cheap, something like $8/day, I think, you could call a cab to take you to AMTRAK, that probably is going to run you $25 or so from Team Parking's facility, unless they have a shuttle going to downtown St Paul.

TripAdvisor has forums. You might want to post your query in the Twin Cities forum there.

Kelly is closer to Greyhound than Amtrak, isn't it?  I think the Days Inn is the only hotel that might be within free shuttle distance.

Greyhound goes from Duluth directly to the St. Paul Amtrak station. Tickets are cheap. Sadly, I think it runs that route only once per day.

Greyhound is a good idea.  I think there will be plenty of parking, though.