88 RX-7 Convertible Tranny or Clutch ?
 

When I shift into first the engine revs but the car barely moves it takes a few seconds to get going but no power. Then I shift to second same thing it takes about 40 seconds to get to speed but no matter what gear you go in you can't just push the gas otherwise it just revs higher. I am sure this is either the clutch or the tranny but how can I know for sure and how much should I plan on spending?

Most likely the clutch. I am having a similar problem with my 88 rx7 vert, although not that bad yet. I bought a clutch kit for 120 dollars off of ebay (gripforce) and the local tire kingdom said they'd install the clutch and machine the flywheel for 300$. so your probably looking at about 400-500 dollars to fix it if its the clutch.

I had the same problem with my fc when I first got it. I would bet that it's the clutch. I got a clutch kit from autozone for $180, and replaced everything myself...It's a job, but it's not difficult. Just takes time.

Clutch
 

Had the same problem and it was the clutch. When you replace the clutch also replace the slave cylinder.