If I were you I would rather just do it myself rather than bring the car into a shop that offers that kind of service. Not to say that there aren't shops that can do a great job with detailing and restoring but in terms of just cleaning its best to do it yourself but that's my opinion. Plus you can take your time and be extra meticulous in specific areas. You will be happier in the end and the job will be more gratifying.
As far as any tips I might be able to give you and help you out with,
One of the first things that comes to mind is what not to use. I would stay away from any strong heavy duty degreaser that comes in a spray can. Some people might be ok with them but in my experience when I tried testing this stuff it ended up actually permanently discoloring a small area on my intake plenum. I have always liked using Simple Green which can also always be diluted to be safe. When I first picked up my GN at 27K miles it looked like the owner didn't even think about spending a minute cleaning anything underhood so I had a lot of work to do. When I first got all the loose dirt and grime off the valve covers they still didn't look so great so I ended up just removing them and painting them. Just wanted to let you know in case you encounter the same thing. Also, after cleaning, if you want to take it further ArmorAll works well on any rubber hoses, lines, and plastic trim by darkening and adding a little shine. There are better products, but these are products that you can obviously find in most stores.
It's time consuming and you have to be patient and can't expect immediate results. Just try to work on one part or area at a time. But depending on the condition of things, cleaning will only take you so far. Eventually, In order to really get things looking nice some parts will need to be restored or replaced entirely. I'm not sure what your goals are but good luck.
I hope my long post is at least somewhat helpful.