Sylvia Irvin filled her car up to exactly $50 on Friday afternoon for a trip to California for the weekend. “All I can think about is how expensive gas will be once I cross into California,” said Irvin. Irvin gets gas exclusively from Costco, where the price for unleaded was $4.49 per gallon at the St. Rose Parkway location. Over at Sam’s Club on Serene Avenue, the price was around the same. Like Irvin, many people in Southern Nevada have turned to getting gas exclusively at warehouse stores such as Sam’s Club and Costco for lower prices. Warehouse stores offer cheaper gas prices as an incentive to its members, a benefit now worth its weight in gold in the valley. The price for unleaded is now at an average $5.06 cents in Las Vegas, according to AAA on Friday. This is an increase from last week’s average at $4.99. At the Costco Business Center off Martin Luther King Jr. Boulevard on Thursday, Kaila Gay was filling up her tank while the line at the pump was wrapping around itself.…