No, the machine work comes after they figure out if the block is salvageable. An experienced eye will be able to tell some obvious things immediately, such as if it's too rusty to save or if there are any problems that can't be fixed. For example, my original 440 had one sleeved cylinder, something my inexperienced eye didn't pick up until my machinist pointed it out when I dropped off my block. It turned out that the cylinder wall was corroded behind the sleeve, so the block was good for scrap. They ended up selling me a core for $150. If you haven't already mic'd it, they should also immediatly mic it just to make sure that it hasn't already been overbored to the limit.
If there isn't anything immediately apparent, they'll wash it, then mag it to check for cracks, then mic the whole thing as I mentioned before. After that, they should contact you to let you know where you stand before beginning machine work. At that point, they'll want some of the parts so that they can set your engine up for your specific parts - pistons, rings, rods, crank, bearings, cam bearings and freeze plugs. In fact, you might not want to order parts until you talk to them and see what exactly you need.
When you say you can get the work done for under $800, I'd be suspicious, though I don't know what prices are like in your area. My block, crank work and rod reconditioning totalled out to about $1000 and I didn't have any clearancing done for a stroker. Before doing anything, put together a list of everything you want done - several of the more experienced engine builders here on the list can help you with that. Call around to at least three shops to get prices and don't necessarily go with the cheapest one. If you know some people with performance experience in your area, especially racers, talk to them and ask where they got their work done and how happy they are with it. Where possible, talk to other Mopar people (is there a club in your area?), because most shops specialize in Chevy and Ford because of the volume and not all shops know the particulars of a Mopar. The basis of a good engine starts with good machine work. All the best parts won't make a dime's worth of difference if the cylinders won't seal or the block leaks oil all over the place.