Cost of Freelance Miniature Sculpts?

By sculpts, do you mean 3d models for consequent production, one-time 3d printing of prototypes, or mass produced 'final product'? Also, if you have KS in mind and it's your first, I would strongly advice against using miniatures.

In this case I suggest to start with researching manufacturers first. Most of them have in-house 3d artists who will make the models, based on your concept arts. Some of the manufacturers will insist on using their artists because producing a 3d model suitable for molding requires specific experience. Manufacturer that we are currently working with, charges 500 eur for modeling. Freelance artist _might_ be slightly cheaper, but you risk the situation where a manufacturer will tell you that your models can't be produced, and you will be forced to pay twice. Not everything that you can model and 3d print, can be mass-produced with reasonable cost.
Also, do your research about further costs. Like the price for making tools etc. How many models do you have? And what kind of game?

Ouch. Well, you're then looking at the very least at 100K+ EUR just for the models. And that's only the tool+modeling costs.

Now imagine production cost (starting around 80 eur, probably more). Add shipping. What will be the price of the box? How many backers will be willing to risk that amount on a 1st time project?

Friendly advise: start with standees. If the campaign goes extremely well, you can always consider minis as stretchgoals.

13 is doable. Then again - you can always have those in stretchgoals.

Though the sum can vary, depending on the method and material, 5-10K is waay too high for a single sculpt. Sure, it's expensive, but not THAT expensive.

Alternately, build your game around an existing line of figures, like Reaper's Bones miniatures. If I recall, they have supplied miniatures for at least one KS project in the past. Too many people are dead-set on unique sculpts, but it's really not very enticing for the consumer if you don't have an established IP, rock solid branding, and/or a really unique of kitschy aesthetic. For plenty of gamers, skeletons is skeletons. The price point is what matters.

As ElKobold implied in his excellent advice, you are far better off building a fan base and some brand recognition with a smaller project, like a 52-card deck game or a minimalist standee 'economy' version based in your IP, before you bankrupt yourself doing such a logistically complex project.