Going back to the question of what you can sell for, we sell whole hogget for £100 each, so £130 is a fair price if yours are heavier. Our butchery is by weight and I can't remember the slaughter charge offhand, but it's under £20, plus like Sally our butcher uses the same abattoir so no extra charge for collection. Our abattoir is about 25 miles away.
We only get animals slaughtered which are not up to standard for selling for breeding, so we are not looking for a profit on them as you are, and in fact most go into our own freezer. We like to sell enough to cover our costs. As you want a profit from the enterprise then you are at a great disadvantage from the beginning with such high slaughter and cutting costs.
For adding value to your product, the breed counts. If you have a rare breed, or sheep raised on salt flats, or heather or whatever, then you can use that as a selling point for higher prices. You could sell whole lambs for spit roasting, same with pigs. If you are killing large numbers then you can advertise online where the prices seem quite high. But you can't get out of the slaughter costs.
Perhaps you should be looking at your other costs, for example raise your meat animals on grass alone, rather than with hard feed. Is there another butcher who would do the cutting cheaper, but to a good standard - there's little worse than chips of bone in meat from sawing while frozen and customers will not buy it?