There are companies which will take your stone and laser drill a microscopic hole in it and literally suck out an inclusion to improve the clarity. They then backfill the hole with a substance which has similar refractive properties as diamond, and only your jeweler will know its been drilled. Most guarantee the process for the life of the stone, and as long as you tell future jewelers that your stone is filled, you should never have a problem. Many people use this technique to improve the quality of inherited stones, but you can also buy clarity enhanced stones from your jeweler and get a nicer or larger stone for less than you would spend on a non-enhanced stone. But be aware, clarity enhanced stones are generally worth less than stones of the same quality which are not clarity enhanced.
Volume can be cheaper.
A cluster of small stones can be less expensive than one big stone. Its because the larger the stone, the more you pay per carat for it. The half carat will cost you more. The larger the stone, the more you will pay per carat. So if you are on a budget, but want something impressive, buying a smaller center stone and surrounding it with a splash of smaller stones can make for a knockout piece of jewelry which costs considerably less than one single diamond.