I really like Lowe's for home projects. Their selection and prices tend to be better than Home Depot, and I also like the way the store is laid out. The lighting and signage in the store is great too. You may not think that matters, but when you're in a store the size of these stores, with 100,000 different products, I think it really helps. The only thing I dislike, is they tend to be a little more nitpicky with returns than Home Depot.
The $50 is just average per trip to the store.