Might be worth considering NOT putting a monetary value on the miles, since there is no standard consensus on this issue. Further, the value of miles vary wildly depending on how you use them.

For example, a 25K domestic coach award is worth $125 if you fly roundtrip from Cleveland-Baltimore with no notice because Southwest competes in that market, but Cleveland-San Francisco with no notice could cost upwards of $1,000. So, destinations and notice afffect mileage value.

A 100,000 mileage bank could be used for a Business Class ticket to Europe or Asia that would normally cost anywhere from $3000-$7000 depending on time of year and destination. That same 100,000 could be used for 4 25K domestic tickets that could be valued as low as $500 or as high as $4000 (see previous parapgraph)!

Instead, why not just focus on the quantity of miles. For example, for purchases/services you provide up to X dollars= 25K miles; Y dollars= 50K miles and Z dollars= 100K miles.