It's possible to resharpen an end mill by hand but it will almost
certainly cut with only the longest flute, like a fly cutter. If you
want to regrind them try to do most of your material removal by
plunging down to preserve the side cutting edges which are much harder
to sharpen. You can also bevel the corners a little and limit the depth
of cut to the bevel. Rough the part almost to size with a reground
cutter and switch to a new one for the finish cut. Time vs Money.

I use a ratty old $100 surface grinder to resharpen end mills, reamers,
taps, side milling cutters, wood planer blades, etc. It has easily paid
for itself by letting me use $1 dull tools instead of $20-$40 new ones.


jw