Heat up your rim bead with a hairdryer and use narrow gorilla tape, start at the valve and lay one strip all the way round, work it well into the rim and bead with a tyre lever then with the wheel fitted to the bike (upside down of course) turn the wheel by hand and trim the excess gorilla tape from the rim bead socket with a sharp scalpel blade or stanley knife, make a small hole and fit tubeless valve, fit tyre, fill with fluid inflate and go ride feeling smug that the entire exercise has cost you less than £5 per wheel.
I’ve ran tubeless for over 12 years with the above method on many different rims.