RegEX Help Needed

I think this can be solve using RegEX, I think so, but I have no idea

Let say I have some variable like this:

$var1 = "cheap"

$var2 = "32"

$var3  = "6"

$var4 = "6"

$var5 = "8"

$maintext = "price is cheap, 16 button, 3 lines, size is 5k x 10k"

I need to check those var against the maintext.

For $var1, find and replace word after "price is ".

For $var2, find and replace word before "button"

For $var3, find and replace word before "lines"

For $var4 dan $var5, find and replace word after "size is "

So the final text will become: ""price is cheap, 32 button, 6 lines, size is 6k x 8k"

If not found the pattern, do not replace any text/words/string.

Any help and code example would be very appreciated

Thanks!