It is unlikely that a natural gas conversion could be done for this price. The tanks to hold natural gas are quite expensive and I doubt we will find a significantly better way to build a high pressure tank than we already know about.

Then you have the issue about a filling station.

Then considering taxes on fuel are nearing 50% of fuel cost, you're right around where this conversion gets you. (I don't know if NG at the pump would be taxed)

Electric solutions work around the issue of fuel cost and filling locations nicely. Electricity is cheap and basically available in every garage. If you have a garage. Having a hybrid electric works around the issues of limited range and cold weather.

I'm just thinking people would fill up at home. If nothing else use it for commuting. Most Americans already have a natural gas line coming into their house.

So charging stations wouldn't be necessary and taxes wouldn't be an issue either.

In the US, Utah and Oklahoma have a lot of natural gas cars, and kits are easily and commonly available everywhere.

So if you are looking for prices, check companies located there.