Photography is an expensive hobby My recommendation is that you go out and by the Pentax SMC FA 50mm f/1.4 lens for your K-r. It retails for around $250 to $350 in Australia if I've done my research correctly. Taking the aperture down to f1.4 (or even f1.8 or f2.0) is going to give you a lot more light gathering ability. This should let you increase your shutter speed with only a minor increase ISO thus avoiding the grain. Note that this is not a recommendation for that specific lens... I looked it up because I know you are shooting with a Pentax K-r. There may be a Sigma or Tamron lens which works just as well for less.

The other option, of course, is off camera flash. I picked up a Yongnuo YN-467 for $52 (currently being sent back because it died) and a YN-560 for around $75 off of eBay. The YN-560 is still going strong and I have my fingers crossed. I'm hoping they'll replace my 467 as soon as it finished taking the slow boat back to China. In any event this is the least expensive way to add light to the situation. Oh, that and the wireless remotes rf-603s for $40 solve many lighting problems but add complexity of understanding and using flash.