I have a minimum of $300 in materials which doesn't include my time, profit, equipment, water, utilities, license, taxes etc. Not to mention the hours, travel, shows and training I have invested in.
Shipping is unpredictable at the moment and suppliers have been hitting taxidermist with surprise increases lately. The few guys I have spoken with in my area range from $500 to $700. I will be honest, the $500 one is absolute junk. It is dry preserved with bondo ears, looks like a drunk 12 year old with carpal tunnel mounted the thing in 30 minutes. I was actually shocked when they went up on price.
$1k commercial quality whitetail shoulder mounts will be common sooner than later. Some of the bigger shops in TN are already $900, which from a business stand point is what they should be at to turn a slight profit.
As for show quality, that is subjective but your going to have a lot more hours in it. Not to mention you'll be using competition quality eyes and replacement nose (open mouth will be much, much more), those two will add an extra $100 to the piece. Most will be using expoxy for earbutts and skull cap, some altering of the form will add extra foam cost. Add in habitat, etc and its not uncommon to have 40+ hours and over $1k in materials for a show piece.
I would clean toilets at a truck stop for minimum wage before I'd mount a deer for $275.