Frankly at this price I think it's pretty much a safe bet to invest now and hold. I consider anything under 500USD to be long-term a fine investment.
Yes I think this price is quiet affordable to invest money into bitcoins, as I hope that the price would be on the top in the future, so its good if we buy some bitcoins at this price.
If you are satisfied with current price then you should buy it, as I don't see it going more low in next couple of weeks, as anything around $400 is good price to buy.