Let's assume that team labor is free
I'm really looking into casting hot glue right now. We could make a mold using a pristine roller (we'd order an extra set of 12 to replace rollers that we mess up beyond repair) -- I believe there are commercial products for building reusable molds for stuff like this.
Further, by using hot glue, it might be possible to simply re-heat the roller (I'm not sure what the maximum temperature of AM roller before damage is done is) to remove the hot glue before re-casting the glue around the roller (we would use this as a roller-repair method).
An added benefit would be the knowledge of how to perform a casting.
Looking online, it appears as if enough hot glue to last us for many years can be obtained for $10, and most of the materials for making molds is around the same price, putting this process well within our team's budget (and freeing up funds for other projects).
We will be putting in perhaps a kilometer or two of mileage on these wheels on asphalt each year. The more I think about it, the less it seems like wear will even be an issue.
I'll propose that we simply buy AM mecanum wheels (probably 8-inch) and, if necessary, attempt to repair the rollers at the end of the year by casting hot glue around them. I'm not sure if casting hot glue like this would even work, but if it doesn't, then we can simply buy new rollers to replace the old ones.
Thanks for all the advice.