J.S.
I don't know of a playgroup, but I do know of 2 venues that have spanish "classes" that are more reasonably priced. One is "Mom & me Spanish" at Studio 59 on rte 59 in Naperville. It's on 59 near 127th street. You can find info on all classes offered there at: http://www.musictogetherofnaperville.com/
Another is Artes Infantiles in Bolingbrook. Artes Infantiles offers several class options all of which are bilingual. And the teacher, Ms. Franchie, is really fun and engaging. http://www.artesinfantiles.com/
Good Luck!