I suppose if you're limited on space/going through a lot of fluid, you can go for something liek this. where 25 gallons costs about $10 (assuming water is free).
http://www.amazon.com/303-230371-Instant-Windshield-Washer/dp/B000FF76KM
http://www.amazon.com/303-230371-Instant-Windshield-Washer/dp/B000FF76KM