You might be able to get a discount if you buy a 'bundle'. This is a great way of getting everything you need at a discounted price. For example, you might buy a certain set of tools and then get a mortar mixing tub and a small step ladder to complete the deal and get the best discount.
Overall, there are a lot of different ways to save money on your purchases. You should be able to save a lot of money on your plastering tools without having to do much. By shopping during specialty sales where everything is discounted, you can save a lot of money.