Interesting. One can play around with this. 1) no way alchemy could do it because chemical reactions do not change elements into another.2) you need to start with a stable isotope of Mercury, lead, etc and end up with a stable isotope of gold. 3) you need to make your starting material unstable could add a neutron. 4) you can decay either by alpha particle (2 at. no, 4 at wt) or beta particle (-1 at. no, 0 at wt.) I spent some time fiddling around and the one way I got starts out with platinum, which is more expensive than gold -(.

Pt (at. no. 78, at wt, 196) + neutron (0,1)= Pt (78,197) unstable
Pt 978,197) decay = beta particle (-1,0) + Au (79,197) stable gold

LOL. There is still no such thing as a free lunch. Not only would you convert a more expensive metal into a cheaper one but the cost would almost be prohibitive as you'd need some kind of particle accelerator to ye olde atomic juggling act.