Can you advise me of any decent but not overly expensive hotels in Downtown Seattle?

Moore Hotel, $74 + tax per night, free wifi, nice hotel.

http://www.moorehotel.com/reservation.html

I stayed there in November. I had to swap rooms as the wifi wasn't working in mine due to the building being very old and historic but I found a room with a clear wifi signal and all was good.

Other than that you can get a private room at the Green Tortoise (on request) for less than $40 but you share a bathroom. I loved the Green Tortoise, best time of my life.

The end of July and first part of August is the peak tourism season. The annual Seafair Festival culminates in that time period, the weather is statistically the best and the hotels charge the maximum. What might fit your criteria also depends on your definition of "decent" and "not overly expensive". So, here are some suggestions from more expensive to less expensive along with a link for each where you can see ratings and read reviews:

About $200 per night:

Mayflower Park: http://www.jdoqocy.com/click-3939914-10775740?URL=...

Red Lion http://www.jdoqocy.com/click-3939914-10775740?URL=...

Hotel Max: http://www.jdoqocy.com/click-3939914-10775740?URL=...

About $150 per night:

Roosevelt Hotel: http://www.jdoqocy.com/click-3939914-10775740?URL=...

6th Avenue Inn: http://www.jdoqocy.com/click-3939914-10775740?URL=...

If you need something for less than $150 per night you can find something near the Seattle Center about 1 mile away from Downtown but fairly easy to get to and from on the Monorail: http://www.squidoo.com/seattle-monorail

Here is a one in that area:

Mediterranean Inn: http://www.jdoqocy.com/click-3939914-10775740?URL=...

Check out www.airbnb.com

You will be able to stay in downtown Seattle in a nice apartment, for way cheeper and with much more character than a hotel.