Lennon was a genius musician. Even he passed away for so many years, but there are still millions of people in the memory of him. You are one of them, and I think you may love him so much that you want to wear glasses like his for souvenir.
http://www.framesdirect.com/framesfc/John_Lenn on-lamcoi-pr-l.html In this site, there are many glasses like Lennon's. I hope you can find what you want there.
John Lennon style round eyeglasses are very common style glasses. You can find them just in normal store. However, considering your budget, I strongly recommend you to buy them at a chain store. A chain store can provide you low-cost eyeglasses and good service. Compared with the online store, you can obtain professional optometry and after-sale service.