This whole event is absolutely horrible. No real way to farm and the cost for one single duel in the Blue Eyes Cup is at least 4 or 5 Duels against SD, since the number of letters you get is abyssmal.
No real way to farm? There are several ways! And Duel-Cost was low enough that i have finished the event (with all rewards min x3) yesterday evening...
There is realy no need for bots...
I had about 200 letters left over from the days before the Blue-Eyes-Cup. Then the first run with a simple Blue-Eyes-Deck with Kaiba's PeakPerformance.
Since the second run i use Mariks SylvanRa-Farm-Deck. If you play this right there is a 95% win rate.
So you see, there is no need for bots, just a little thinking ;)