MYSQL - 具有最低值和其他条件的SELECT行，或具有最高值的回退

there seem to be a lot of threads here asking similar questions, but I'm yet to find the one that helps me solve my problem.

I'm trying to select a row with the lowest value where three other conditions must be true OR fall back to another set of conditions, given a variable (uc) and select the highest price.

Table: level (sample data)
id  |price  |copies |used   |uc
--------------------------------------
1   |7      |10     |10     |charlie01
2   |17     |10     |8      |charlie01
3   |37     |5      |5      |charlie01
4   |47     |10     |9      |charlie01
7   |5      |15     |9      |charlie02
8   |15     |15     |0      |charlie02
9   |35     |15     |0      |charlie02
10  |45     |15     |0      |charlie02
11  |3      |5      |5      |charlie03
12  |13     |5      |5      |charlie03

Results: EDITED RESULTS - charlie01 should be 2

VARIABLE    |RESULTING ROW
--------------------------
charlie01   |2
charlie02   |7
charlie03   |12

### START Pseudocode: ###

Select the row with the lowest price where used is less than copies and used is greater than 0 and uc equals VARIABLE OR IF NO RESULTS (which means all the used are equal to copies) Select the row with the highest price where used equals copies and uc equals VARIABLE

SELECT * 
FROM level
WHERE

    (
        used < copies
        AND used > 0
        AND uc = *VARIABLE*
    )
 ### OR IF NO RESULTS ###
    (
        used = copies
        AND uc = *VARIABLE*
    )

ORDER BY price ASC
LIMIT 1

### END Pseudocode ###

This is the query I wrote (using uc charlie01 as an example):

SELECT *
FROM (
    SELECT *
    FROM `level` 
    WHERE 
        ((
        `used` < `copies`
        AND `used` > '0'
        )
        OR
        (
        `used` = `copies`
        ))
        AND `uc` = 'charlie01'
        ORDER BY `price` ASC

        ) AS T
ORDER BY `used` ASC
LIMIT 1

It doesn't work on the sample data because of record 3, even though used = copies. This is because used on record 3 < used on record 2 (the row we want, because it has the lowest price)

I know MAX() exists and have tried for the last hour to use it, but with no success, I really don't think I understand how it works, It seems to just be selecting the maximum value of the whole column no matter what...?

Now, I've gone round in circles adding conditions and such, but I think I need to do a JOIN of some type but I'm not really sure where to start with it. How do you think I should go about this query?

EDIT: I'm really sorry, I just realised I was saying highest price when I was actually trying to select the lowest price where used < copies BUT the highest price if all used = copies

Cheers
Charlie