It really depends... If you think you have a good grib of clients, and loosing one extra client that doesn't approve of paying for customer tech is fine with you... then it's ok... But as a startup, I advise you to put in atleast 18-20 hours online waiting for tickets, support, etc. Have a friend to help you out, take turn, shifts.

LOL,, I think $1 for 24x7 support is tooooooo low and $1 per incident is toooo high !
LOL, I dont know how will things work out for 24x7 support for $1 ! and we all know there is no limit for issues in hosting industry to go with $1 per incident basis..

A fixed price although will be a better idea ..!

$1 per incident too low ?
wow, tech support staff must be *real* cheap where you are - $25 per incident is too low IMHO