I think something like this will better adapt the subsidy to the actual need and widen the benefit to more situations - specifically in places where computers are present but upgrades to more powerful ones are needed. Here's a couple of ideas we might use. Computers that are replaced using these funds must be given to a computer pool. I think it should probably be more than one value depending upon the usability of the machine which is turned into the pool among other things. An amount could also be made available to subsidize 1st time purchases or replacement of much out of date equipment if computers from the pool are not adequate.
Fewer dollars can serve more people.
Discourage frivolous upgrading when current system does the job. Keep the option of getting a used computer for free attractive.