Perhaps first out of cheap dress (3,4)
I believe the answer is:
low gear
'perhaps first' is the definition.
'low gear' can be an answer for 'first' (I've seen this in another clue). I'm unsure of the 'perhaps' bit.
'cheap dress' is the wordplay.
'cheap' becomes 'low'.
'dress' becomes 'gear' (I can't justify this - if you can you should believe this answer much more).
'low'+'gear'='LOW GEAR'
'out of' acts as a link.
Can you help me to learn more?
(Other definitions for low gear that I've seen before include "It's needed on steep hill" , "one crawls along in?" , "for hill-climbing?" , "Shoes and socks" , "which is needed for hills" .)