It's not the speculators that caused oil price up: global demand is up due to skyrocketing demand in China and India etc, despite slowly declining demand (due to high prices) in US and Europe. And NG prices are down, not up, at the moment, in the USA. Temporarily, since they are now below production cost, and the producers are therefore slowly winding down drilling etc, while demand is increasing as electrical power producers are switching from coal to NG, and truck fleets convert to CNG/LNG...
But back to PV prices: the price in US dollars may increase due to two possible future scenarios: rising cost of NG (to make the electricity to make the PV panels), and a decline in the global purchasing value of the US dollar (assuming that the US Fed prints money faster than everybody else, and that Congress gets its wish and the Chinese let their currency appreciate). Another issue is the demand for PV, it's been depressed due to the economic problems in Europe, but may build back up, especially elsewhere, e.g., in China, India, Brazil, Saudi Arabia and other Persian Gulf states (yes they are building huge PV arrays), etc.