cant {plug} then redrill, 50.00??
not many real gunsmiths, would touch that rifle for that money, and get it right.
if its trully off that much, weld the hole, then redrill. a bit more then 50.00
however.
most if not all real A4,s are drilled off center, as the rear bridge is off center to the center of the reciever ring.
the new China made bases are bent as well, and likely need bending to fit right.
remove the base, and see if your holes are indeed center with the muzzle.
a little off may be ok, and windage screw adjustments can fix that..

FYI: most if not all real gunsmith shops have a min, fee for work done.
standard is 75.00. mail order work may be more depending on the smith,
and turnaround time can be long...
i like to get things done, and on the way home within 3 weeks.

heres some standard rates..{not mine} of most gunsmith work.
drill and tap a hardened receiver. 35.00 per hole. plus set up time.
to clean, and safety check...75.00 min.
headspace check, and some{testfire} 50.00 plus shop time.
thats a run across the board flat rate...some may be more, some may be less.
all in all you get what you pay for..that being said.
mosts low dollar work with take 6 mos, to a year to get your gun back.
and even then, it might not be right...hard to find a smith that knows 1903,s 1917,s and other WW2 US weapons.