a community of practitioners
This arrangement normally works for someone starting out with no/a small book of business. The more established you become the less this will favor you and can make you sick to your stomach like you said unless you can negotiate some really favorable terms. Ask if they can throw in insurance for example as they already have a business policy which will come at a more favorable cost and allow pre existing conditions. this is just one example. try thinking of similar things you can have them throw in that you can piggy back off of if you really want to negotiate a fair deal. If not, get a room of your own and pay a flat rent. You will be better off over the long term.
How about taking a percentage with a cap such as 50% per massage with a $300/month cap that would be equivalent to room rent and any amount beyond that goes to MT? 100% after the cap is reached paid to MT.
There are tax advantages to paying rent, i.e., deductible as overhead on your taxes, vs. working for a percentage, i.e., the "room rental" is not deductible for you on your taxes. It is more predictable to have a set dollar amount for rent than to have a fluctuating amount for rent. Also, thinking down the road, once you build you clientele at the chiro's office, what is to keep him/her from changing the arrangement so it is more advantageous to him/her? I would suggest leasing an office outside of a chiropractic environment in a part of town that is (1) close to your home, (2) in a neighborhood affluent enough to be able to afford regular massages, and (3) with a contract in place clearly delineating each and every aspect of the agreements made by both parties. If you do decide to go the chiro route, be sure to find out how many other therapists he/she is going to hire in addition to you, because that can significantly diminish your potential income, and also determine in writing who is going to provide the massage table, the linens, the lotion, the sound system, the marketing, etc. Also find out if the clients are "your's" or "their's," so when you leave you will know whether or not you can take the clients with you. If you go to a lot of time and trouble to market for clients, only to find out that the chiro considers the clients as part of his/her client/patient umbrella, then you are stuck at ground zero and have to begin building your practice all over again. It can be a real hassle if you have to share your room and set up your own table for every client you see. Also ask yourself if you like giving 15-30 minute sessions; I personally prefer 90 minute sessions in my own office.