Candles are the most cost effective way to decorate a room. Check out Ikea's glimma tea light which last for 9hours. This avoids relighting on the party night. Ikea sell clear glass holders which fit the glimma tea light as they are slightly larger than the average tea light. You could pop a few scented tea lights in here and there to create a nice scent but not too many as this would be overpowering!!
photo source stylemepretty.com