Regarding the cost ... if you're not already aware how much it costs to build a trail, you'll fall off your chair when you find out.
I worked for the engineering department of a shire when the longest trail in Victoria was being built ... and my shire was responsible for the portion of it that went through the shire.
Home - Great Victorian Rail Trail
We're talking million
s for that trail.
And that's just building it.
As has been mentioned, there's also the aspect of maintenance.
If a shire can get a healthy grant from the government or a benefactor of some sort, and if the shire is financially healthy enough to handle maintenance, then great ... build a trail. Many of Victoria's trails are quite nice. But if the OP is planning to "finance and support such a system with a use tax" ... assuming a relatively short trail only costs $1 million, the OP had better hope a minimum of 100,000 cyclists use the trail.
Yes, I would recommend getting involved with trail building ... find out what's really involved.