My best finds in the wild:
Italian Polly (white body, pink hair and hearts) for $3 tops the list. I walked away from that table (antique fair) in a daze. She had a pink saddle on and some part of an outfit so it wasn't immediately noticeable that she was a non-US pony, let alone one that was so special. I thought she was a faded Peachy at first.
My other more memorable finds were Hollywood, Munchy, Yum Yum, Taffeta and Pristina for $3-4 each, and a good bundle of accessories in a big ziploc bag for $6 (assorted big brother, twin and princess accessories).
My best online finds? Probably lavender Woosie MIB, I think I paid $80 or so?
Otherwise I would say most of the second set sea ponies and their shells (Sand Dollar etc) cheap hiding in lots or BINs on eBay.