i've had many customers (add) a little extra to their check when they pay for their quilt (and i'm not as *inexpensive* as yours!) i charge a pretty reasonable rate- but often if i give someone an invoice that says...$135 on it I may receive a check for $150...I do charge for batting (at cost) if i provide it- most of my customers bring their own choice of batting. I do not charge extra for thread unless i'm using a specialty thread- or making many color changes.
i don't think it's unreasonable to add a bit if you think its worth more to you than you are being charged and you can afford it.