Hiya!
I think it is reasonable to charge more for very unique and one off items.
Looking at your shop, I think it is quite confusing to have identical styles all listed as unique and one offs at various different price points. I think if you use a variety of different fabrics with different costs, it's better to find a price that represents either the average or the highest possible cost for that item and charge it across the board.
I used to charge different prices for silk and polysilk, but I finally decided that as the main cost in each piece was the labour anyway, it was less confusing to customers to charge a single price.
Maybe you could use fabrics that you can re-order to produce your usual lines such as coin purse, shoulder bag, metal frame clutch,etc so you can keep each style at the same price point, and then produce a luxury line made of one of a kind fabrics which have a unique overall shape AND the OOAK fabrics. These can then be priced significantly higher than your day to day lines and become your showcase or aspirational pieces.