Generally Lowes does have culled bins too, though I think they're more prevalent in HD. Even if they don't, a 2x4-8 is only $3 or so, so you won't spend much more than what Hauntcast did in its video to pick up the supplies off the shelf.
You could even try 2x3-8's too, they're a little bit cheaper and a bit lighter than the 2x4, though you might want to make some bracing from your scraps to make sure the table remains solid if you'll be doing pounding on it. Otherwise you'll be fine with it as it is.
Also, find the straightest pieces possible at the outset because it will make your life so much easier when building. There aren't any old growth trees around these days to get lumber from so the new growth lumber tends to warp a lot. So starting with a straight board first means you'll have less work to do later and your project will be better at the end.
Many times you have to pull a lot of pieces of lumber off the rack to find the straight ones. Sight down along one edge to see if it's straight and then flip it one turn and look down along one face and you'll see right away whether the board warps or not. Boards can look straight when you look at them from the side, but looking down one edge reveals its defects. Good luck!
"but his blood will I require at the watchman’s hand." - Ezekiel 33:4