I don't think a modest increase would be unwarranted as you grow your business and improve. Other contemporary companies have had price increases over time (look at UK). CUSTOM contemporary companies are similarly priced and your product is 'different' than others in the marketplace. I think if people are looking at your kilts, a modest price increase would not put them off.

As you grow and your costs / overhead rise, you see that what you need to charge goes up as well unless you can cut costs or improve speed in other areas of the business. Its a balancing act and as one area increases, something else in the business has to give, whether it's price, quality, speed, your own pay, cutbacks, etc.

If you're worried about price increase, perhaps a % increase across the board may be better than a flat $25 per model.

Another way to 'lessen the blow' (as someone else mentioned) is to have free shipping for a set period with a kilt order.

So long as you have a quality product and are asking for a 'reasonable' price for it, people will be willing to pay for it.

Best of luck with whatever you decide!