SOLVED. YA fiction- boy finds money (British decimalization?) & buys birds. [s]

[Emma]

I read this book at least 10 years ago but I think it was old at the time.
The book is about a boy finding a bag of money (maybe it fell off of a train?) that is about to no longer be spendable because the country is changing to a different currency system (maybe it was related to the UK going decimal?)
He goes on a spending spree that includes buying all of the birds at a pet store & releasing them.
I don't remember all of the details but I think he may have had a deceased mother & a difficult relationship with his father. I think his family had moved houses which he resented & he returned to their old house to mope.

[Rosa]

Millions

[Emma]

Rosa wrote: "Millions"

That's it!! Thank you!

[Rosa]

You're very welcome!