...and those boards aren't cheaper. The OP in order to get beefier power supply will have to get a cheap mATX board, which means it will have only 2 RAM slots and worse chipset.
Since the OP says he was going "very budget" build, it is unlikely he is going to go SLI/CFX and since he already has an i5-3450, overclocking is impossible so the h77 chipset would be every bit as good as z77 at this point since both of the z77's advantages over h77 are forfeit anyhow.
As far as DIMM slots go, go to NewEgg, go to "More" search parameters, select LGA1155 and micro-ATX, search, open the "More" menu again, select Number of DIMM slots and you will see that the number of LGA1155 mATX boards with four DIMM slots is larger than the number of mATX boards with only two slots. When I tried this a few minutes ago, I saw 41 quad-DIMM models vs 33 dual-DIMM so the majority of mATX motherboards (on NewEgg) support full DIMM complement, no sacrifice from going mATX there unless you specifically make that choice.