Hi,
sorry for late reply, it was weekend for us

No sorry you can't do it.

But you can do this:
create field "Choice of subject" with these options for example:
- Option 1
- Option 2
- Option 3

create "Select the price" fields for each option of "Choice of subject". so you can create "Select the price 1", "Select the price 2", "Select the price 3".
Now you can set conditions
if "Choice of subject" is equal to 1 show "Select the price 1"
if "Choice of subject" is equal to 2 show "Select the price 2"
if "Choice of subject" is equal to 3 show "Select the price 3"

Same way for "Timing classes" field

But the field is displayed on each option "Choice of subject"

1) I create field "Choice of subject"(select) and
- Option 1
- Option 2
- Option 3
2) Create
(text)"Select the price1" for - Option 1
(text)"Select the price2" for - Option 2
(text)"Select the price3" for - Option 3
3)
a) in Paramater - Condition - Equal
Field to compare - "Choice of subject"(select)
Custom Value - 1
Target Field - "Select the price1"(text)

a) in Paramater - Condition - Equal
Field to compare - "Choice of subject"(select)
Custom Value - 2
Target Field - "Select the price2"(text)

a) in Paramater - Condition - Equal
Field to compare - "Choice of subject"(select)
Custom Value - 3
Target Field - "Select the price3"(text)

Have I done?
But it opens all Fields

Hi,
in "Field to compare" you must set "Custom Value" and customize your custom value, you want compare "Choice of subject" with a custom value

Unfortunately your suggestion does not suit me!

This option is suitable for the function SELECT, and I need a checkbox. Selecting multiple objects and separate prices for them. Do you understand me? If you could make the parent field, it would be fine.

Hi,
when you put option into select/checkbox/radio fields you set something like this (value|text)

0|Option 1
1|Option 2
2|Option 3


you can create these conditions
if contain custom value (set to 1) show "Select the price1"
if contain custom value (set to 2) show "Select the price2"
if contain custom value (set to 3) show "Select the price3"

you can use contain instead equal