Unfortunately, I don't think that you will find both at the same place.
For price, you have to go to a big box. Home Depot, Lowe's or Menards will give you the best price on your "general" supplies: 2x4s, plywood, kitchen & bath fixtures... Now of course this all depends on what your budget is. You will also find a greater variety of products, ready for you to take home that day.
The flip side is, good luck finding someone that knows anything about what they are selling. if you are looking for product knowledge, then you should visit the respective "specialty" shops for each item. An employee at a stand-alone paint store (Benjamin Moore, Sherwin-Williams) will most likely know more about paint than someone at Home Depot.
Now, there are people who work at HD, Lowes and Menards who are very knowledgeable about their product, and if you find those people, remember their names and find out their schedule, they are rare.
The best reccommendation would be to acquire your knowledge about plumbing at a plumbing supply store, then go to HD and make your purchases. Go into a specialty tile store, learn all about ceramics, travertine, granite; play with some designs, then go to HD and make your purchase.
Now, depending on how guilty you feel about wasting other peoples' time (some of those specialty shops are commission based), you will probably only be able to get away with that once or twice. Once they've determined that you are not going to be making any purchases with them , they won't be as willing to help you with all of your questions.
A nice middle ground would be your local lumber yard, they are smaller than HD and Lowes, don't handle as much product (so their prices will be higher), but generally, have better customer service.