I would suggest getting the C9. Yes I agree the slide on the .380 is pretty sharp looking compared to the C9, but you have to take a few things into consideration as well. What are you using the weapon for? Are you going to use it for target shooting, home defense, personal carry, ect.
If you're using the 380 for target shooting that price difference in ammo adds up fast! Where I live I paid nearly $30 at Wal-Mart for a 100rd box of 380 ammo (Winchester). Ammo prices differ from state to state, but you're going to shell out more in the end.
If you're using the 380 for a home defense weapon, and an occasional plinker, then I say go for it

As stated it doesn't have the stopping power of the C9, but in a CQB situation in your home, a 380 round would do the job. (even a .22lr in CQB within a home would be effective)
I have the 380 and I've enjoyed it greatly, but she just got too darn expensive to shoot. She was retired to a home defense weapon, and I now have her up for sale. It was the first HP pistol I bought, and at the time was looking for a cheap reliable pistol. One thing I never really understood is why the 380 is in the HP line up. One main purpose of the 380 round is for a "smaller more concealable" weapon design. The HP380 is freakishly large compared to other makers. I tried to carry it concealed and it took me less than 2 minutes to decide NOT to leave the house with it concealed as it looked like I was carrying a brick. I've open carried it, but even then it was quite heavy in the holster for that as well.
Good luck.
Squeak