What one does need, is dear a penny

Hi everybody!
Pleased to meet you. I'm a Spanish free-lance translator and I'm just happy that I've found you ;-)
I hope you can help me with this sentence:
"Nothing is cheap which is superfluous, for what one does need, is dear at a penny".
I think I've understood its meaning (perhaps: superfluous things are always expensive; necessary things are not). But I wonder if it is a phrase used in specific situations and even if I have undestood it correctly.
Thanks in advance.
MARTA

Dear Marta,

I have a different understanding of the phrase. I think it means that nothing that isn't a necessity is can be considered cheap because what one absolutely needs is expensive.

Imagine an unemployed person offered an ridiculously cheap price for a trip to Spain. Unfortunately because this person can barely pay for the necessities, so it doesn't matter how inexpensive the trip is, it can't be considered cheap.

'Dear' is used here in the sense of expensive.

I haven't heard the phrase used before. Where did you find it?

I haven't heard this phrase either. The first part is easy to understand. If you buy something useless at a reduced price,(like a ship in the desert), it's not really a savings. You've wasted your money.

I'm having trouble with the second part. If you really need something (like a heart transplant) it is cheap at any price. But "what one does need, is dear at a penny" doesn't say that to me. One of the meanings of "dear" is "expensive." ("Dictionary of Word Origins: the Histories of More Than 8,000 English-Language Words" by John Ayto; Arcade Publishing, New York, 1990). Something you really, really need wouldn't be expensive at a penny.

R. Berg? Can you clear this up. I've muddied it enough.