Help DIY or professional gardener

Last year I moved and obtained a relatively large garden that is very mature with a few trees and requires quite a lot of work doing.  I have previously grown my own vegetables so was keen to just set aside a section of my garden to do the same this year then over the next few years work on a section at a time.  My other half thinks that we should ask a designer to tell us how to set out the garden, but I'm worried about cost.

Can anyone give me a rough idea on designer costings and perhaps other people's experiences?

Many thanks