I did 2 evictions (placed by the same property manager, lol). The first one was handled by Loeffler Law Group, second one - Dimensions Law Group. I can recommend both. I would not try to do eviction myself, there are so many things that could go wrong and you'll have to restart this process again (in the best case) or will have to pay fines (in a worse case).
Total eviction cost depends on many factors, e.g. if you need to go to the court or tenant settles, default judgement vs hearing, etc. In my case, we could negotiate with the tenant and eviction didn't cost too much. You can request price sheet from both companies and compare.
Another company, which I didn't use personally, but was recommended by several people I know - LT Services.
+1 for RHAWA membership. It costs about 200/year, but you'll get resource desk, which respond in 24 hours and would cover a lot non-trivial questions. Plus lease for WA and Seattle, and a bunch of addenda. Plus a lot of online classes about landlord-tenant law, about operating rentals, and investments in general. Plus forum. Totally worth it.