Smartphone - cheapest? (Android)

What is currently the cheapest Android smartphone? I would prefer unlimited data but don't need it.

I heard that there are many deals around April for new University students. For example, Softbank had a deal for the iPhone 5s for 3000 yen a month in March (usually 7000 yen per month).

called gakusei waribiki 学生割引

Ion nexus4 is 2,980 YEN(include a smart phone) per month with 24 months contract, unlimited data usage with 3G 200kbps(unable to watch Youtube).
http://www.aeonretail.jp/campaign/newcom/

Only available 8,000 lines(phones). It's on sale from 4th April at Ion supermarket, it's already been sold out 30% of it stock.

Thank you Tokyo Friend. That is a good deal and I would have bought it, but they only accept credit card and I only have a bank account.

It might be possible to use a Visa debit card from Suruga bank, Mitsubishi Tokyo UFJ bank, Risona bank etc for the payment. You can have a visa debit card if you are 16+ age. But I've never used a visa debit card for the payment so not quite sure. Docomo, Softbank and au don't accept a visa debit card payment.

Thanks for the suggestion. Unfortunately I do not use any of those banks.

I will probably get the Nexus 5 for 41,000 yen (2500 yen per month for 5gb data).

^ unless if there is something cheaper that can be purchased with a bank account.