So if you sold for $1m and bought a property for $400k the IRS would look to tax the $600K you didn't spend.Since you don't have excess cash you may want to consider something like a Delaware Statutory Trust which will absorb your debt with the institutional financing of the sponsor.

Have you considered Delaware Statutory Trusts?

This is my first 1031 Exchange and I’m learning from it If you cannot find anything to buy, you might want to consider investing in one or more Delaware Statutory Trusts (DST). 

@Daniel Sherman, you can utilize a Delaware Statutory Trust (DST) for your boot.

Perch Wealth offers realestate brokers an opportunity to introduce an alternative institutional investment to their 1031 exchange clientstypically through a Delaware Statutory Trust (DST).

If you are not able to find a suitable replacement property - there are some passive investment solutions (ie Delaware Statutory Trusts) available. 

An option for the exchange considering her mental state may be a Delaware Statutory Trust (DST).

I'm not an expert with 1031 exchanges but I believe there is a way to move into a passive investment through a Delaware Statutory Trust.

Are you referring to a Delaware Statutory Trust, or a deferred sales trust?

Does anyone have their properties held in a Delaware Statutory Trust (DST)?