You should consider the following:
- What is the effect? (Blood/Gore, CG character, set extension, cars, lasers, spaceships)
- The expected result - How good does it need to look? (movie quality, high end TV, low end TV, student film).
- What skill set is needed to accomplish the effect? (3D modeling, rigging, animating, compositing, particle simulations, miniatures vs 3D models)
- The experience of the artist quoting you the numbers. What credits to they have?
- The number of days the effect will take this particular artist to compete the work.
- The number of revisions you expect to make (0-10?)
- How close is your deadline?
- Will the artist be present when the footage is shot? Do they have the experience needed to make sure it's done correctly? Do you?
In the end, it really comes down to days. What's the rate? How many days can you afford to put into the shot?
A senior artist may cost you more money, but they are able to suggest several options on how to accomplish the effect within your budget. They should also have a similar effect or technique they can show you on their reel. An inexperienced artist may do the gig for free (to gain experience), but will be making it up as they go. A newb is also more likely to get stuck, frustrated, and quit.
I'm curious, what exactly are you are looking to create?
