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Motorola Moto E (2015)
If there's one company which can deliver as impressive low cost phones as Nokia and now Microsoft it's Motorola, and the Moto E (2015) is one of its most affordable yet at around £90 SIM free.
It's perhaps the closest Android competitor to the Lumia 635 too, with 4G support, a 1.2GHz quad-core processor, a 5MP camera and a 4.5-inch screen.
Yet it trumps Nokia's offering in a number of ways. For one thing that screen is a little sharper at 540 x 960. The Moto E also has twice as much RAM (1GB) and a VGA front-facing camera, which isn't up to much but is a whole lot better than no front-facing snapper.
However it's also ever so slightly more expensive than the Lumia 635 and for better or worse it runs Android 5.1, not Windows Phone 8.1.
Microsoft Lumia 435
The Microsoft Lumia 435 is the first 400-class device in the Lumia range and as such you won't be surprised to hear that it's one of the cheapest at around £55 SIM free.
That makes it significantly cheaper than even the Lumia 635 yet surprisingly it's actually better in some ways, with a front-facing camera and 1GB of RAM rather than 512MB.
But inevitably a number of sacrifices had to be made to achieve that price point. There's no 4G for one and it only has a dual-core processor. It's also got a smaller 4.0-inch screen and a weak 2MP rear camera.
Despite losing out in a couple of ways the Lumia 635 is clearly a better phone then, but it's hard to argue that the Lumia 435 isn't good value for money.
Microsoft Lumia 640
If you can break the £100 barrier then the Microsoft Lumia 640 is a worthy alternative to the Nokia Lumia 635. It's newer and at around £130 SIM free it's significantly more expensive, but it still falls into the low end of the market.
There's a lot to like about it too, with an impressive 5.0-inch 720 x 1280 display, a long-lasting battery and a decent 8MP camera.
It supports 4G as well, so price aside it's an equal or better phone than the Lumia 635 in just about every sense, though in most areas it's only a modest upgrade.
It's undoubtedly worth the money, but if you're on a tight budget you won't miss out on much by choosing the cheaper Lumia 635.
EE Harrier Mini
The EE Harrier Mini is the successor to the surprisingly accomplished EE Kestrel and with a price tag of just under £100, coupled with 4G connectivity and Wi-Fi Calling, it's a tempting little phone.
It's locked to EE of course, which could be a deal breaker right there, but if it's not you can look forward to a respectable 4.7-inch 720 x 1280 display, an 8MP camera and a near stock version of Android 5.0.
That leaves it with a clean, uncluttered and intuitive interface, which you can customise to your liking while dealing with minimal manufacturer bloat.
Its performance sometimes feels a little lacking (though on paper it's actually slightly more powerful than the Nokia Lumia 635) and the 635 is a little cheaper, but it's a good option if you want stock Android on a budget, especially if you're already an EE customer.