I have no stocks at all right now, no IRA, no bonds. $7000 cash (rising) and $3000 in low-interest student debt (from wife, falling). I save $800/month and put $500/month toward said debt, on top of all bills.
Is there any reason I shouldn't buy a few thousand in index funds soon?
That depends on what you expect the market to do, how your research supports your expectations, and what your goals are.
My goal is "return OF capital", and I seriously expect a major bust and shake-up in the markets due to the fraudulent monetary games being played by those "students of the Great Depression" who either should know better, or do know better but are duplicating history because they or their buddies are in a position to profit from it.
If I'm wrong, I'm out the ~7%+/yr loss on capital due to inflation, but otherwise have liquidity. If I'm right, well, I have either liquidity, or a lifetime supply of toilet paper.