Local cuisines of Phnom Penh is similar to Siem Reap. And you may find cheap Cambodian dish at Capitol Restaurant in Street 182
For nightlife experience, you can try the Sports Bar in Street 172 west of Street 51.
And for beer tasting (which was part of our itinerary), try the Cambodian Beer.
(you may check our budget and itinerary for this trip – Thailand, Cambodia & Vietnam Tour)