Well, yes. But the airport and it's parking is rather a ways from downtown. If you're flying in and staying at the hotel, you could actually park in long term at the airport, and ride the max around Portland. It's a very Mass Transport Friendly city, Portland is.
SmartPark is on of the options, as well as many other parking lots and structures in any part of town you want your car in while you're at the con. But I don't know their prices.
My mother tells me they've raised the prices at the Smart Parks, but, again, we don't know for sure.
Street parking is actually free after 6pm on Saturday and free all day on Sunday, if you can find a spot.
You might try going on Portland's website to find out better info.