Well, an infinity-focus FD to EOS adapter is likely to cost you in the region of £20 to £30, with no guarantees about the quality of the optics.
The FD 50mm f/1.4 can sell for between £50 and £70 without too much difficulty if it's in good condition.
For about £70 to £100 (i.e. the difference between the sum of your costs and opportunity cost) you can buy a brand new EF 50mm f/1.8 Mk II.
Granted it's not in quite the same league as the FD or EF 50mm f/1.4, but you get a warranty, autofocus and little uncertainty about the standard of the end result.
Received wisdom four or five years ago, before a deluge of cheap FD-EOS adapters appeared on the market, was that it definitely wasn't worth the effort.
If you have a lot of other FD lenses (and you intend to continue using them with your A-1) it might be worth looking at. If it's just the one, I'd suggest it's still probably not worth it.