First of all let me say how great it is to see you step up and look after your boy like that, you should be real proud of yourself im sure it was an emotional journey..
Where abouts in the world are you living? If I was you, I would try and get in touch with a local Dieatician and they would be able to help you sort out a meal plan, and give you loads of nice recipies..
What are your sons recommended phe levels? How many Exchanges is he currently on? If you post this information up, it would make suggesting foods a little more easy.
My partner is currently on 17 exchanges (she is pregnant), therefore she has 17g of protein to play with each day(1g of protein would be 1exchange), which she feels is quite alot.. more than she would normaly have. An example of a dinner meal for her would be:
2 Sausages (6 exchanges)
225g potato (5Exchanges)
If you want to private mail me your email address I would be more than happy to send you a copy of the food lists we recieve from our doctor which will give you all the different types of food and how many exchanges they use.
Here in the UK we get free Health care. So it may not be as easy for you to do what I do. We get alot of PKU foods and drinks through Prescription from our Doctor. There is many different types of cake mix, biscuits and choc bars available through companies such as SHS International. Again we get these through our free health care system so im not sure of the cost issue.
I Wish you all the best and hope both you and your lil man stay happy and healthy..