"You get what you pay for" is absolutely true... but... I want to offer some advice that goes against what you've been seeing. Take with a block of salt!
With a personal project like yours, I understand why you don't want to sink lots of money into it. If you can honestly say you'll be happy with another pair of eyes on it, even if it's a beta reader or someone in your social circle with an English background, then go for it. Barter your services--either read for them (like Old Hack said, you can't really harm someone's writing. It's on them to utilize your feedback and grow as a writer, and it's your responsibility only to give them your reactions to their story), or organize some other work swap if it's someone you know locally.
It's all about knowing what you want and what you'll be happy with. I've met lots of writers who want to self-publish their memoirs, not for the market but for their families, and I can't imagine them plunking down thousands for professional design and formatting and editing when all they want is a box of books to pass out to their grandchildren. You always have the option of producing your book through a print on demand service without ever making it publicly available, too, if you don't want to deal with your book getting purchased randomly by strangers.
Just my thoughts. If I had a personal project such as yours, I'd find someone I already know with an English background, or someone that one your kids can vouch for, then offer an exchange based on around 20-30 hours of work (depending on the length and how clean your manuscript already is). They prepare to spend up to 30 hours on your project, and in exchange you provide (a week's worth of freezer meals, weekly babysitting sessions, or whatever). I would also shamelessly get my adult kids involved in this, too, but that's just me. (Mine are the munchkin variety, but I'm optimistic about how eager they will be to help with all my creative shenanigans).
It's not free, but it won't cost money. And honestly, if you won't be satisfied with the results this way, then don't bother and find an editor with professional experience and plunk down the cash.
It all comes down to knowing what you really want and what you'll be happy with.