[adrianhoward]

This is heavy handed, as is the client using this type of negotiation tactic. It's not healthy to respond this way.

Possibly I'm getting less mellow with age :-) My responses used to be more like yours, now I tend to be a bit more direct.

The ones who are approaching it purely as a negotiation tactic don't care or mind - they understand what the issues are and appreciate cutting to the chase.

The ones who really don't value my time I don't actually really want as clients...

However you approach it - and your approach is completely reasonable - the key realisation is that this isn't a question of the client not having the money to pay $dayrate. This is most likely a pure negotiation tactic to get a drop in the quoted rate.