Will be travelling from Iguaszu to Sao paulo in Mid July and would like to know any long-distance Argentinian bus service available form FoZ do Iguacu. Also would like to know journey time ,cost and Bus service websites. Any advice on this issue will be appreciated. Thanks.

Have you considered flying? There is a direct flight 5 days/week via Aerolineas - in March it was quite reasonably priced. ($135 or so as I recall)

Yes, Its almost $250 per person for flights departing around 7.30pm on July 13.

Right now, I see a fare on the GOL site for that date and time (a Friday fligth at 7:20pm)of R$214.90 (U$107.83). And midweek is only R$137.

You are traveling in Brazil. Why use Argentine airlines or bus companies which may be more expensive?
For many routes in Brazil, and especially in low season (including July), many flights are competetive in price with the bus these days. I know that for Iguacu to Rio, for example, the bus is about $200 and the plane is about equal, so Sao Paulo should have the same price conditions.
This particular journey is long and not very scenic, so it behooves you to fly and maximize your time in seeing more important sights.

Thank you VidaNaPraia & Elizabeth
I have booked my flight from IGU to GRU.
VidaNaPraia--> Thank you for searching fares for me GOL.