The e-visa is not (yet???) available at DME . There is an international transfer facility at DME, but continuing to LED means domestic connection -> need for regular visa. As it seems you start in LED, but from there to MOW visa is needed.
Also if you manage to construct a two-segment international trip, connecting with something like DME-MSQ-LED, all travel from MOW to any Belarus airport for some reason counts as 'domestic' and a visa is needed.
Economy fare with AY is only slightly higher through HEL, €173, than S7 with fares from €148 through DME (possible to get at €141 with awkward timing and 36+ h layover at DME). The total cost with a regular visa is higher, and considerable more time-consuming.