I've also researched the topic on various forums on the topic of "cheap but good Gaggias" extensively before buying a barely-used Carezza on eBay for about USD $120".
The old Gaggias are almost all the same internally. The higher end models (Classic, "old" Baby, Baby D...) have a 3-way solenoid, whereas the lower end models don't have the solenoid (Carezza, Evolution, Coffee Deluxe). Other than the solenoid, better external construction, variations in water tank size, and in some cases passive cup warmer, there is absolutely no difference between the high end models and low end ones. All of them have the "commercial brass" lower group, and the aluminum boiler upper group, with 1425W heating elements on the outside of the boiler (apparently less chance of calcium deposits causing problems with this design).
The new Gaggias can be divided in two groups. The higher end models (Baby Twin, Baby Class, New Baby) keep the same design as described above, but add a couple of new features such as touch-sensitive controls. However, the lower end designs (Pure, Color, Dose) have been revamped completely. The brew group is now stainless steel, and the heating elements are on the inside of the boiler, which requires less power (1100W).
From what I know, the only difference between the Color and Pure is the color of the plastic housing. The Dose adds dosing capability (able to pre-program a button with a precise water volume to brew).
Some people say the revamp is the influence of Gaggia having been acquired by Saeco. There is some debate on whether the new design is better than the old one. Some people say the old design is superior since the design is "tried and true", having been the standard Gaggia engineering for decades, and parts are very readily available, and their replacement well documented on the internet.
There are many "old Gaggias" available on eBay and at various US online retailers (example:
www.wholelattelove.com/gaggia.cfm ) . I'm not sure if those available new have been sitting on the shelf a long time since those machines have now been discoutinued.
If you are looking in Canada, I saw a brand new Evolution at "Centre du Rasoir" in Montreal for $430, right in your price range.