It doesn't help since the M10 won't meet your needs on the internal mics, but the increased cost of ownership shouldn't be too high. At least in the U.S., we can pick up from both Energizer and Duracell (and probably a lot of other brands) a rechargeable AA battery charger and 4 rechargeable NiMH AA batteries for $20.
Since 2 of the AA's will run the M10 for 30+ hours, you'd wouldn't even need the other 2 AA batteries you buy in the set. So you'd have a new set of AA batteries for you favorite TV remote along with the batteries you need for the M10 for $20.
The DR100 mkII might be just what you're looking for. Another option might be the Sony D50, which is the big brother to the M10. Unlike the M10 though, the D50 has directional mics, with the option of 90 degree and 120 degree placement. You can often pick them up used on ebay for $350 or so. Plus the $20 for the AA charger and batteries of course.