So starting with the $50 Celeron G1820... is it a better buy than the Athlon 5350? Keep in mind you can purchase LGA1150 H81 boards for as little as $50, so the build cost is the same as the Athlon 5350 with an AM1 board.
In our application tests, the Celeron G1820 was 20% faster than the Athlon 5350 on average. Moreover, it was 63% faster at encoding and even 10% faster in our gaming tests. With that said, the G1820 consumes 45% more power, so it comes down to whether you care more about performance or power consumption.
Given that the extra power scales pretty well with the extra performance that you will see, the Celeron G1820 seems like a no brainer. For the same $50, AMD offers the A4-4020 which is a 200MHz higher clocked version of the A4-4000 we tested with, and given how that performed the G1820 shouldn't be threatened.
Jumping from the Celeron G1820 to the Pentium G3220 probably isn't worth $20 more as we didn't see a 40% boost, with the biggest gains being ~25%. Meanwhile, the Core i3-4130 is up to 85% faster than the G1820 (generally ~40%), but the i3 is 150% pricier. If you can afford it, the i3 offers a better experience.