The cheapest muscle-building shake will typically be a mixture of dextrose or rice flour, protein powder, and milk. This is a simple and effective mass gainer that is definitely not the most healthy, but does offer similar benefits to a mass gainer at a lower price and with a good nutrient profile for building mass. You should also add some sea salt or pink salt to improve electrolyte content. It’s optional – and can be gained from diet alone – but is a great bonus.