I've got fond memories of my Funk & Wagnalls Science encyclopedia. It was "my" encyclopedia - it wasn't useful for all school projects, but it was great to just read. As opposed to the school library's encyclopedia filled with topics I didn't care enough about to read through linearly.

I never associated it with being the budget option, but I don't think my set was comprised of different editions either. Also I think my parents could have afforded a Britannica if they had been turned on to the idea, but they were drawn to buying things incrementally from immediate sales channels. You're spot on about the marketing. I remember them always being prominently at the front of the store. From what I remember the first book was $1 or free with a grocery purchase or something like that, and then of course after reading through that I bugged my Mom to get the next one.

(Also I can't help but notice Macaulay's "How Things Work" on the bookshelf in the article. Another hands-down classic that I would definitely push towards kids today even if they don't take to encyclopedias. I believe he's written a follow up book for modern tech, too)