One place where you should spend the coin on a budget build is the pistons. If the rotating assembly is balanced properly the stock rods will be ok assuming they have been treated, good rod bolts etc. Head studs and a multi layer gasket like Cometic is recommended.
Nothing wrong with Mahles (forged) pistons mate. Have them in my engine.
Got mine from the US for about $1000 when the dollar was good.
Average price for a good forged piston is about $1350.