i have seamless aluminum gutters on both house and barn. Prices vary widely according to size of gutter and gauge of aluminum. I paid about $400 10 years ago to have thin-gauge aluminum gutters installed on the house, no leafguards, smallest size gutter. Leafguards would have doubled the cost. Probably around 150' or so total length, but broken up into 5 separate gutters.
I paid $1500 to have large, heavy-duty gutters, with leafguards and kind of fancy round down spouts installed on the barn this fall. Total run is 100" with 5 downspouts. The lafguards and downspouts were about $500 of that amount. I did get a quote of $660 from another vendor for the small, thin-gauge gutters with no leafguards.
I went with the higher-priced installation for several reasons. First, you can lean a ladder against the heavier gauge without damaging it or worrying about it pulling loose. Second, the roof is 10-pitch, and water splashes over smaller gutters, large size is better. Third, the barn is next to, and shaded by, a line of trees on the neighboring property, and the leafguards are practical. Finally, the fancy round downspouts, for $65 extra, just look cool. I'm in a historic district and things like that, while not required, get noticed and appreciated. Which gives me a little credit to fall back on if anyone complains about the milling noises