I am not sure about that "best price gauruntee" thing but I have always found great deals through Competition Products. They only deal in engine stuff and they offer everything from cheap "claimer" assemblies to full blown race units with 5000 dollar short blocks.
They would definately have something to fit your budget and application.
For durability I would go with a Big Block. Even the stock 2 bolt blocks with cast cranks were good to 600HP and 7000 rpm so they can really take a pounding.