NBAA 2008 Jet II (10-20k lb MTOW) Copilot:
Average: $47,575
10th Percentile: $30,000
25th Percentile: $40,000
Median (50%): $47,000

For a "typical" entry level Citation/Lear SIC position, I've heard everything from $25k to mid-50s. Personally, I think a lower-time pilot with no turbine experience and no ATP should reasonably expect the upper 30s or low 40s (higher if in SoCal or NE) as a starting salary.

Of course, if you can negotiate more then by all means do so!