Wool blankets are one of the main items I look for at garage sales, thrift stores, and antique stores. Textiles are usually pretty inexpensive when you find them used. Wool blankets might have a high price tag, even at a thrift store if they are considered collectible. Hudson Bay blankets with their heavy fulled character and stripes are usually at the high end, along with Pendleton blankets. Garage sale prices are usually less than thrift store prices. The most common issue with thrift store wool blankets is moth holes.
With liquids, prompt spot-cleaning can often take care of fresh spills and stains. If you need to clean dust and dirt off of a wool blanket, try shaking it out or brushing it before you attempt to wash it, since rigorous washing can damage the blanket. If you spill anything on your blanket, try to blot it away as quickly as possible.