In addition, the company has shown off its first voice-controlled smart screen for the home to feature a camera.
This allows it to offer more personalised features than a previous model, but also risks provoking a privacy backlash.
Other announcements at its annual developers conference included enhancements to its search tool.
The Pixel 3a and larger Pixel 3a XL will cost £399 and £469 respectively, making them roughly half the price of the seven-month-old Pixel 3 originals.
Until now, Google had charged one of the highest entry-point prices for an Android handset, with its basic model costing £70 more than Samsung's Galaxy S10e and £40 more than Huawei's P30, and no option to buy a "mid-range" alternative.
The new versions share many of the features of the more expensive Pixels, including OLED (organic light-emitting diode) displays for rich colours and the firm's much-lauded Night Sight facility, which uses machine-learning based artificial intelligence to enhance images taken in low-light conditions.
In addition, they will also provide use of Google's new augmented reality maps, which superimpose arrow graphics over views of the scene ahead. This, the firm claims, will make it easier to judge which direction to set off in.