The effective repellency of Lymeez lasts for about 600 hours of use. ($0.05/hour) Use the chart below to estimate how long a pair will last depending on your level of outdoor activity.
In contrast, spraying pants with permethrin is generally far more expensive as shown in the chart below.
Furthermore, since sprays only last 40 days, there is quite a bit of repeated spray applications to match Lymeez 600 hours of use. For example, if usage was 10 days a month for 2 hours each hike, it would require 30 sessions of outdoor spraying to reach 600 hours of use. It would cost 3 times the amount of Lymeez for the spray alone, plus the time and effort of 30 spray sessions.
And, after all that, you would still not have the 4–8X slow down effect of the 3D Mesh.
(Full spreadsheet analysis, 156kb PDF.)