I love i5s and this is only $30 more than a i3. It will have plenty of speed for everything you need and more.
Intel Core i5 3470 3.2GHz LGA 1155 Boxed Processor BX80637I53470 - Micro Center
If you really want a budget build then i3 all the way. Most computers that are designed for office work, like
Word/Excel and light internet use i3s. Yes, the onboard graphics is plenty.
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