I put both the 3 gallon Solo backpack piston sprayer and the 2.25 gallon handheld professional sprayer (has a carry strap and pressure release that the 2 gallon non-professional version lacks) into my "save for later" Amazon cart. Since both are sold by Amazon, I figure there's a chance they'll go on sale during Prime Days (July 11 & 12). The handheld is currently 20% off, but we'll see.
https://www.amazon.com/dp/B00208ILSI/
https://www.amazon.com/dp/B000V4M4QS/