Use a guilded altar in a POH (player owned house) with both burning torches or candlesticks. To find a guilded go to a "house parties" world and go to a popular place near a house portal like Yanille or Rimmington. The most cost effective way is regular bones (cheapest). The most popular used bone is the Dragon bone around 5.5k which grants 252 experience at a guided altar with both lamps lit. Depending on the bones you use will depend on the cost. Some people take about 200m to get to 99.