The Honorable normal guy way:
depends on the length of the track and the complexity of it.. and the work you have to do.. from scratch or an edited version.. and also your work time fee.. most people add their work time fee to the work finished product.. as the manufacturers in our daily lives .. others charges only the product price.. or their price/hour so if u spent around 2 hrs composing it.. wold make you a whooping honorable way ... 30/100 bucks if its less ... you can still be in that range... the end use or ur client wont ask u why is that price so hard... if so.. u can always find excuses.. but most people that are hobbyists dont have cash flying around... so id better stay at a lower price.. for helping them out.. and maybe getting some publicity and get another order
The Business Type of audio sales:
(its not accurate but more of a guide.. of what the actual licensing goes for audio products.. they might be a bit different but this is a simple rough shape of it )
you can also sell it as a non-exclusive license.. so you can resell it further on internet without any problems.. audiojungle for example .. also you can give a limited-exclusive license.. that gives 1-3 months of usage before you sell it further...
the basic is this...you can sell it .. as regular license (for hobbits non monetized products)
limited-personal license - you can use it for a longer period of time making cash with ur product using the audio in it.. but not reselling the audio..
Personal license -buyer gets to partially own it.. he can resell it/ and make cash out of its products with the content of audio inside up to some sort of number records (ex 1000 sales in steam etc ) while you can still sell your own
Business license - buyer is eligible for selling your audio further as a vendor
Custom licenses - charging fees per product hit.. example ( 1mix license ... buyer publish in one video /game etc u need 1 license 30 $ or what ever, 2 videos or games he needs to re-buy the license for each product he releases)
custom license mix - u can use the original soundtrack to derive a new version .. each remix adds more licenses
and so on
hope it helped you .. and i was on track of your post