Ask HN: Equity/cash arrangement for new social app?

Hi folks, wondering if I can get your advice. I'll keep details short since you probably don't care about the story behind this situation. Basically, I've developed a working relationship with this person over the past few months. She's one of the best thinkers & doers I've ever met. I would be giving zero thought to this if I didn't care about working with this person. Right now, we're considering building a social venture that would require native apps for ios and android. Given our history and mutual respect, we've discussed a 50-50 equity split. But there's an option for me to go for less equity for some amount of cash upfront. Realistically, I don't think this social app will ever make any money. But because it's going to be native, the value of the development (that I'd be doing entirely) would probably be between $40-80k (at the very least). The question is...I don't think it's fair for me to create this much value when I doubt I'll get any in return. But if I ask for cash in place of some portion of equity, how do I value this venture that doesn't exist yet? I doubt there's a straightforward answer here, but I welcome your thoughts and/or resources to help me figure this out.