Bicycle Mechanics - Changing Fron Chainrings

I have the standard 53/39 front chainrings on my Shimano Ultrega crank.(10 speed) I would like to change them to smaller rings maybe a 50 or whatever is the smallest for the larger ring and to a 38 for the smaller ring which I understand is the smallest ring that will fit there. Where would the best place to buy these on the internet. Also I have no idea what they might cost.

I've found good prices for chain rings at nashbar.com, loosescrews.com and bikepartsusa.com. You will be looking for 130mm BCD crank rings. Ebay is also a good source if you can find someone selling both sizes you want at once, else shipping can eat into your savings over going to a retail shop.

btw: figure about 15-25 for the inner ring, and about 30-35 for the outter ring + shipping from most online shops. loose screws has a 46T and 48T outter ring if you really want to go that low, they also have a 50T outter that you mentioned above. They've got a 38T inner for you as well.

btw: figure about 15-25 for the inner ring, and about 30-35 for the outter ring + shipping from most online shops. loose screws has a 46T and 48T outter ring if you really want to go that low, they also have a 50T outter that you mentioned above. They've got a 38T inner for you as well.
Thanks for the quick info. I just went to the loose screws site and found the chainrings. They seem to be one piece and the info says "no ramps or pins" I think mine are multi-piece and has some pins. Are these the ones you are talking about. The 50T is $28.50 and the 38T $22.50.

Another good source is http://www.sheldonbrown.com.

yeah, I forget all this new fangled stuff they put on new rings these days. ;) (My newest crank is a 7speed 105 crank) :p