Amongs the cheapest, Thrasher, Catalyst, Coercer only.
If for some reason you want to use Caldari ships then Cormorant but you will basically need at least 1 more than you would need catalysts which will not make it cheap in the end. But doable, 3x t1 cormorant should be able to kill retriever in 0.6 (if untanked) or 0.5. But since it is just destroyer, ship you can train in 1day and you don’t need to skill it to lvl 5 because Catalyst doesn’t have bonuses to dmg you only need lvl 3, there is really no point using Cormorant.
Not sure about Coercer cost but Thrasher is cheapest. However, thrasher is not exactly best choice for ganking miners, thrasher is good on gate against small ships or industrials.
t1 Thrasher comes at 1.5milion, t1 catalyst 3m (because rigs are expensive), t2 catalyst around 13mil