I did a high pressure fuel pump on my HHR SS with a 2.0T LNF engine. ZZPerformance had "take-off" parts for around $350. The high pressure solid metal fuel lines running to and from the pump are supposedly single use, but most people have successfully reused both lines without an issue, add another $100 or so if you order those lines as well. 
Changing the pump is about a 30-45 minute job. It's located right on top of the engine on the right side of the head. It's as simple as removing the engine cover, a few mounting brackets, and a noise damper cover. You'll then need to bleed the high pressure line via the schrader valve, unscrew the fuel lines, remove the electrical connector and finally remove two bolts to take the HPFP itself off. Once it's off, you'll want to check the cam follower for any scoring or damage which might indicate you have a cam problem as well. If it looks good, oil up and replace the the cam follower and slap the new pump on (pay attention to the orientation marks on the new gasket), replace the other bits and you're done. 
One word of caution, a lot of LNF engines had supposed HPFP failures and replacing the pump won't necessarily fix the problem. Apparently there's a known issue with corrosion of the electrical connector for the HPFP so this should be looked at first prior to spending big money on a new pump that you may not need. If you google around the Solistce/Sky forums or HHR/Cobalt forums you'll find a lot of information on HPFP replacement. The best indicator that your HPFP is toast is fuel pressure that sits around 50-70 psi on the high pressure side. This indicates that the in tank pump is working but that the HPFP isn't building pressure, the car is also unlikely to start if this is the case. With a working HPFP you should see 200-300 psi at idle on the high pressure side.