K-Mart, Sears or other stores like that have paint that's less expensive than paint stores for the exact same paint/color. You mentioned painting the interior and exterior, a couple people chimed in on the outdoors so here's something to consider for the interior. Gloss/semi-gloss, textured walls/ceilings, are any of the rooms for children (if so get a "wash-able type). Having done this with a spray gun and by hand, if/when I have to repaint again, I'll be using brushes and rollers. The spray gun was fast in getting the job completed but the paint smell lingered longer verses the brushes and rollers. As others have mentioned for the exterior if you can afford it, avoid the cheap $8-$10 gallon stuff - unless you want to repaint in a couple of years. The only problem I had, and this is age related, was doing the ceiling but once got the extender rollers, it wasn't that bad (but I wouldn't want to do it again for a while). A professional service will save you the work factor and you'll get a guarantee on the work for 'x' number of months/years but this is something most people can do themselves. Lastly, and this applies for both indoor and outdoor painting, buy a couple of extra gallons (of each) for touch ups so there will be an exact match. Hope this helps.