It's strain dependent on how much you will yield. Some plants will get more than others. Figure a baseline of 10-20% of what you wash, you'll yield. 20% being the high end, and it's gotta be some frosty, dusted with powdered sugar looking buds. On 10 washes this Year so far since harvest. I'm averaging around 14%, and they were some frosty plants, that have produced some dank hash that everyone wants. I'm the only person making hash around me, and am getting bugged all the time, "got anymore, wanna sell some, can you give me some???"
My best investment wash a set of bags and washer, 1 run by hand, and said F¥€£ that!!!!!!!!!! Then started shopping, you can get the same exact washer that the "Bubble Bag Dude" sells for half of what they sell them for.
I suggest watching the hours of Frenchy Cannoli videos, absolutely valuable info and insight.
Just smoked some that I pressed and tucked away, and its crazy how much better it is than just dried and smoked, but either way, it's still better than smoking flower IMO.