Ammeter to Voltmeter...who does it?

Im interested in converting my stock ammeter to a voltmeter and was wondering which companies can do this, and approx how much they charged?

I did a search and saw that redline does it for about 140, but I'm trying to see if anyone has any experience with other vendors?

I thought about doing what some people have done and use a 1 1/2" volt gauge and retrofit it into the dash, but I didn't really like how it looked installed next to the other gauges.