When we researched where to stay cheaply in Portland in August, we found that there were seveal motels near the airport in the $60 range. Even though there is excellent public transit, we weren't too excited about staying half an hour (on public transit) from downtown. We decided to try our luck on priceline. We did our research (using sites like bidfortravel.com) and ended up getting a room at the downtown Hilton Portland and Executive Tower for $70 a night!
The location is great. When we arrived there is parking right outside the hotel for 10 minutes - we got a free upgrade to the executive tower just by asking. The rooms are larger, and we were on the 18th floor with a nice view of downtown. The room was impeccably clean, the linens were luxurious - this was a big step up from our usual accomodation!
There was a couple of downsides. The parking is expensive at $18 a night. There is no free wi-fi, which was surprising for a hotel of this price. The Executive tower (located kitty corner to the main building) has no pool, just a lap pool with a small gym. The only way to get to the main building is to walk outside and cross the street (a 2 minute walk).