Cheapest way would be to higher a contractor with machine guidance already on his excavator. Send him your coordinates in SPC, and away he goes......

A job made for machine control.  But if your machine operator was set up to do that you would not be asking this question. 

I've done a bit of forestry work.

For an experienced planter 500 pine bare-rooted seedlings is about a day's work, or perhaps two.

Why do you need the excavator?

What is the required accuracy? This maybe done with a consumer grade GPS if only need 30ft accuracy.

Hire a surveyor. At some point in the future, location will matter for 500 trees.

I.e. Say 200 of the seedlings die before maturity, were they all from the same vendor?

5 trees, what the heck.

500, yes, hire a professional to tie points to property line or to some reliable and established base.