thoughts on retrieving broken ...

thoughts on retrieving broken drill string

I would question the value of retrieving this drill string.  You have a used drilling bit, assumable, but you didn't mention it a weight collar on above the drill bit and then you have what sounds like trash drill pipe.  Assuming the drill pipe is of zero value due to too thin a wall and a history of breaks, I would suggest you spend your time and money obtaining new drill pipe.  

Second issue:  A fishing tool such as a female socket with cam action teeth is a very common fishing tool and could be fabricated by a local machine shop.  Think of this as a two meter long section of PIPE which is twice the size of the drill rod outside diameter, make a female taper at the bottom, fit the inside with three cam action teeth which ride up when lowered over the drill rod, then roll down and clamp on retraction.  Lower this device into the hole repeatedly until the teeth engage.  BUT the drilling mud by now has solidified around the bit and drilling wieght so the chances of just pulling this up and out would seem about zero, so now you need to jet down the hole to fluidize the mud.  Good luck