The tenant can decide not to exercise the option and buy somewhere else, or we could lower the purchase price, or the tenant could come in with a higher down if they really wanted the house.  

In any case, I'm curious why the hypothetical scenario here matters - what are you trying to achieve from this exercise?

Juggling building my RE career and running my business has been an exercise in time management, and most of that time for the month I've been licensed has had to go to compliance and training. 

So for a house like this one I would offer them $1625/month + T&I and the balance of $351k due on exercise.

You could also focus on the great financial advantages of renting/down-sizing (travel more, no more yard to care for/repairs, buy an RV, visit family more)Host a senior-focused event at your facility (maybe show an uncut version of Woodstock haha) or live music, a Social Security expert speaker or Doctor to address health issues, a fund-raiser, art show, etc. and hand out flyers with a special "one month free" coupon attached Have exercise classes for seniorsWeekly bingo nightsPromote your events for free on community calendars, newspapers, seniors sections of papersPrint door hangers and get some kids to hang the door hangers at trailer parks, older communitiesEncourage your current tenants to invite friendsRent a 15-passenger bus ($50) and offer free transportation to key eventsSponsor events at senior centers in the areaCo-Sponsor service club (Rotary, Kiwanis, etc who have many senior members) eventsPut up banners and balloons when you have eventsI hope at least a few of those ideas might spark some interest.

A great exercise to plug numbers into to see which option best suits the OP.

If the turnkey is only offering cash purchases, I would exercise extreme caution. 

It basically turns into part of their down payment when they exercise and buy the property. 

It's a puzzle that should induce a coma, but I actually find the thought exercise of it all... stimulating.

Look at it as an exercise or as a game.