There are many written instances in Google Books of...
(some sum of money is a/several...)
...thousand pounds if it's a penny
...or without the pronoun and repeated verb...
...thousand pounds if a penny
But a smooth-talking salesman would never use this expression to refer to his selling price, since his potential customer would hardly want to buy something with such an open-ended final cost.
Where the English expression might be used by a salesman is if he's trying to sell something for much less than £1000...
I can sell you one for as little as £250. But as you know, the true value is £1000 if it's a penny.
In my experience, the English use of £1000 if a penny essentially stands for at least a thousand. But it doesn't normally even imply ...and possibly several thousand, let alone ...and possibly as many thousands as there are pennies in £1000 (i.e. - £100,000). It just literally means If there's any value / cost at all, it won't be less than £1000.