obtaining difference between minimum value and next in size

Hi, I was wondering if it is possible to do this with a single query rather than iterate over all of the rows in an application:

I have a table which for brevity looks like:
create table offers {
integer id;
integer product_id;
double price;
}

where for each product there is a number of offers in this table. Now my question:
Is it possible to obtain the difference between just the minimum price and the next one up per product, so say I have the following data:
id, product_id, price
123, 2, 10.01
125, 2, 10.05
128, 2, 11.30
134, 3, 9.45
147, 3, 11.42
157, 3, 12.08
167, 3, 12.09

then I would like the following returned
product_id, difference
2, .04 (10.05-10.01)
3, 1.97 (11.42-9.45)

,etc

Any ideas?

Thanks

John
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