I'm not too good at these things. All of my art examples and prices in both SP and USD are [here]. Too much? Too little? Every time I change either prices to match the 1-3 conversion rate they look very...wrong to me. Any advice would be very helpful :)

You should definitely consider going for something closer to the 1-3 conversion rate because in my mind your sp prices are way too low. Not that I wouldn't love for art that good to be that cheap but it just wouldn't be fair. ^_^