Wash. Rev. Code § 35.42.220
The annual budget of a city shall provide for the payment of rental that falls due in the year for which the budget is applicable: PROVIDED, That if the cost of the real or personal property to be leased exceeds the amounts specified in RCW 35.23.352 prior to the execution of a lease with option to purchase therefor, the city or town shall call for bids in accordance with RCW 35.23.352: PROVIDED, That if at the expiration of a lease with option to purchase a city or town exercises such an option, the fact that the rental payments theretofore made equal the amount of the purchase price of the real or personal property involved in such lease shall not preclude the agreement from being a lease with option to purchase up to the date of the exercising of the option.
RCW 35.42.220