try go to a shop where the sales owner is friendly enough to allow you to change the next day (in case Dad don't like the color or style...
Tissot has many nice range too...affordable....best place is to surf the website of these brands....Tissot, Ball, Oris (for last 2 brands, your choice limited since budget is slightly on low end).
Once you see 1-2 pieces that you like, come back here and ask where is good place to buy....we can't post directly here but we can pm you....
another way is share with us what style do you think he'll like? outdoor type like Casio G Shock? Dressy watches with simple dial? busy dial? brightly colored? big size?
Don't worry about your budget...a gift to the Dad is priceless! All the best in your hunt!