I'm likely thinking too much in pounds as I'm British, but professional games cost £40 a game back when DC was current, sometimes £30, which was amazing. Most indie DC games are very light on content compared to these titles, but obviously cost of manufacture is higher due to lower numbers and no official support.
As such I'd pay £20 (About $25-$30) for a good to great 2D title, and £30 (about $35-$40) for a good to great 3D title. I'd push to £40-£50 for larger exceptional titles.
Most of the indie titles I've seen are in the $20-$25 range for me. Though I'd love for some peeps to gather and bang out a high end title to lay down legit cash for.