Charging based on looks is a bad habit to get into. The industry works off day and half-day rates, and your best bet is to go with that.
What to consider when figuring out your pricing? Firstoff, you don't want to undercut the other artists in your area. HOWEVER, you do want to price yourself based on your skill level. Given you're still starting out, I'd say work along the same rates for assistants. More important for you right now is building up experiance and your book. Also, asking what the budget is for the gig is a great way to figure out where you want to price yourself in the beginning.
For reference:
In LA, assistants generally are $150-350/full day
In your area (Vegas) assistants generally are $200-600/full day
Not having seen your book, but going off your comments from your previous thread about your shoot, I'd say shoot for the lower range around $150-200/day.