@Isaac Blocher, I think I over-stated my case, and I apologize. If your rehabber will accept your terms with the lien in place, go for it. If they balk, be prepared to take the lien off the table. There's no right or wrong way to structure your deal as long as you're both happy with the terms and everything's legal. Lien issues are significant to me; they aren't to all rehabbers.
I think the LLC approach is the way to go. You're probably already planning this, but in case you aren't, I'd recommend getting an experienced real estate lawyer to review the operating agreement prior to filing. If they're good they'll be able to think of more situations and scenarios that would need to be spelled out in the agreement than you and the rehabber will. For example, what happens if the rehab budget quadruples? Are you legally on the hook to fork over the funds? If so, is there any limit, and what happens to the deal if you can't or won't pay? If you aren't on the hook, what happens to the project if the rehab exceeds your limit?
As far as the split goes, In my opinion you are over-valuing your contribution to the equation. (But again, others would disagree. If you can get someone to JV with you at 45% or 50%, go for it.) While it's significant that I've never put together a JV deal, I've thought about how I'd structure one, and in my opinion you're undervaluing both the effort and expense required to acquire a good deal, and you're undervaluing the work required to bring a project to payday. In my own personal opinion, each part of the equation is worth about a third of the profits: he who brings the deal to the table gets 1/3 of the profits, he who brings the labor to the table gets 1/3, and he who brings the money gets 1/3.
I would be content with such a split no matter which side of the table I was on. For example, if you brought me a deal and the money and wanted me to do all the work, I'd say me getting 1/3 of the profits was fair. If I had funds to lend and someone brought me a deal and was going to do all the work, I'd give them 2/3. If a wholesaler wanted to JV with me for some reason, I'd expect 2/3, etc.
(Note that 1/3 for labor assumes hiring a GC. If I was hiring and managing subs, I'd expect more like 40%, not 33%.)
These are nothing more than my thoughts on the matter. Feel free to disregard any or all of them. :)