Based on the real world crime articles I've read, a hit man gets anywhere from nothing at all (mob boss says, "Kill him or I'll kill you.") or status (gang leader says, "Kill him and you are a fully initiated member.") to around US$50k; typical seems to be around $10k. A Traveller Imperial Credit is customarily defined as about one 1978 US dollar, which is about four present day US dollars, so a $10k hit would be about Cr2500, and a difficult $50k hit would be about Cr12500.
What about the character? Violent criminals are almost always stupid and low status (which is why they couldn't get by with an honest job), so I'd say the maximum Intelligence, Education, and Social Standing would be 5. They tend to be strong, maybe 9 to 11 Strength. Dexterity and Endurance are likely to be average, 6 to 8.
For skills, I'd say Gun Combat-1, Melee-1, possibly Stealth-1, and if old enough also Streetwise-1. If they were good at anything else they'd have an honest job.