I have the 3840 and really like it.
My only advice it to wait for the bags to come on sale on Amazon. Someone will post when they come on sale.
Weston Vacuum Sealer Bags
Sometimes they run them at cheap prices on e-bay as a roll. So, if you plan on cooking for a while...
Go to an Office Depot or Staples, and buy yourself a paper cutter. I like the roller / cutter wheel type as opposed to the guillotine. Then set it on the counter, and put a piece of tape on the counter along one edge - as a mark for your "zero point". ( This way, if the cutter gets moved, you can quickly re-position it. )
Then decide how long you want eh bags to be. Measure this distance from the cutter blade itself to a point that is to the left or right of the cutter. Place a line of tape there. NOw you can pre cut as many as you want - at the size you want them. Seal one end, and you are done. This is cheaper than buying the pre-made bags. But, really only worthwhile if you buy a fair amount of bags - or if you like to plan ahead. THey don't have a shelf life, so….save now!