Based upon what I see in the photo it would be difficult to completely close that space and maintain a natural look. Closing the gap without adding length to the teeth would make them look to wide and unnatural. When adding the length to the teeth it would make them stand out even more and based upon the crowding on the lower teeth it doesn't look like there is room to add length to the teeth. Often the reason for the space between the two front teeth is caused by a heavy muscle attachment known as the frenum. Usually that muscle attachment needs to be severed (very non invasive) and orthodontic (braces) movement is suggested. Traditional bonding however can cost anywhere from $200 to $700 depending upon the number of surfaces being bonded.