I think normal labs do not do the processing themselves for slides (E6 processing) as with last time KT Imaging do not do that themselves until they got a newer machine. You can try sending them to Fotohub, Ruby Photo, Konota or KT Imaging (yes they upgrade and do slide processing now).
The cheapest is Ruby at $4.50, followed by Fotohub and KT at $6++. Konota is $7.50. For push/pull Ruby and Konota do, not sure of the others.