Rimless glasses are more delicate than other rimmed glasses, so they are required to be made of durable material like titanium which is very lightweight and durable. Thus the material of the rimless glasses is more expensive than that of other rimmed glasses. Besides, rimless glasses take the makemanufacturers more time and care to finish them due to their delicate properties, so they are more expensive than other rimmed glasses.
I don't think that all rimless glasses are expensive than other rimmed glasses. There are rimless eyeglasses that cheaper than some full rimmed eyeglasses frames. The rimless glasses are more expensive than some rimmed eyeglasses because the lenses of rimless glasses must be very sturdy. Since there is no frame to protect the lenses, the materials must strong enough and not break when dig a whole for fix eyeglasses frames.
I have worn glasses for many years and I mostly have had framed glasses. My glasses are on the expensive side anyway because they are no-line bifocals. Two weeks ago I bought rimless glasses. With the glasses 'frame' (what's left of it), the lenses, insurance, anti-glare coating and tax, my bill was over $600.00. My other glasses never cost me that much. I sucked it up and bought these glasses because I was tired of having part of my face hidden by frames. I really like my rimless glasses but I wish they weren't so expensive. Also, I got them at Eyeglass World which is usually an inexpensive place to buy glasses. Someone posted on here that on rimless glasses, the pieces are put on by hand and I suppose this is what jacks up the price. My glasses didn't take any longer to make than any other glasses I've had. I guess it's just a matter of style and preference and if you have the money. I had to save up to buy my glasses.