Restaurants in Puerto Vallarta can vary from top gastronomical gourmet dining to the other extreme consisting of small Mexican spots frequented by the locals. Naturally prices will vary accordingly. Some of the top chefs in the world are located here and the locations of some of the restaurants will impact the price as well. Since Puerto Vallarta is located on the side of a mountain going down to the sea, restaurants on the hill have incredible views, which of course will impact the price. Other locations on the beach or offering views of the daily spectacular sunsets can be very pricey as well. These locations will cost you as much as any US (i.e., Phoenix) top quality restaurant along with the ambience to boot. You could easily spend $100 US per person along with drinks.
In the middle of the road ($25-$50 US) there are hundreds of places to enjoy with great ambience and great food that are very attractive to tourists that can be found in all areas of the city. These are often written up on websites such as Tripadvisor, etc., so I encourage you to check them out.
However as an expat living in Puerto Vallarta there are an incredible number of places, be they small dining spots, or even street stands where the food is delicious and may cost as little as $2-$3 US for a meal. I find that while there may be little ambience at these places, the experience makes it all the more exciting. Food is often served in ways unfamiliar to outsiders but that's the fun of living in Mexico! You can always tell the ones with the best food because those are the ones that are always crowded.
So from a cost perspective you can dine out for whatever your budget will allow. My recommendation is to mix it up and try the gamut if your budget allows. If not you can still enjoy delicious food for very little money.
Many tourists who travel to Puerto Vallarta here stay at resorts or hotels that are "all inclusive." While that might sound great in theory it really ends up costing your more and limits the opportunity to discover many great alternatives for dining. If you are thinking of moving here make sure you open your options and try all that the area has to offer.