Oh, that's easy. The most thoughtful and romantic things are free/cheap.
Now, I'm not an overly romantic person, my love language is acts of service, so if I'm feeling loving, I'll cook a complicated meal or on a very rare occasion bake (I hate baking), I'll offer a massage, take care of a nuisance task that I know has been bugging DH or just upgrade something around the house that I know he would enjoy, etc.
DH on the other hand is, uh, kind of excessively romantic, so there are a lot of flowers and cards with deeply moving writing in them, he hides loving notes in weird spots, like pockets of my coats, or stuffed in a pair of socks, so that I find them randomly, he plans whole day-long fun days where he'll scout out and find a perfect picnic spot, figure out a movie I would enjoy, or finds an event in the community, or even all of the above. He's done elaborate scavenger hunts, in the dead of winter he's decorated the house to look like a beach, cranked the heat, insisted I wear a bathing suit, and made summer cocktails because he's a total nutter. He knows I hate having to decide things, so he puts his effort into planning the entire thing so I'm never left having to choose what to eat, or where to go, or what to watch. He makes sure it's seamless and effortless for me.
And that's the thing, it's really the thought he puts into it that has value. We could easily together organize a nice day of things to do, but what makes me feel appreciated is that he puts all of the mental work in for me, I just have to show up and have a nice time.
On the flip side, he is not great in the kitchen and not handy at all, and not the best with boring logistics, so when I take care of those things, he feels appreciated.
Just figure out your DH's love language and do things that fit it. Would he love to come home to his walls covered in ridiculous "Welcome Home" decorations or would he more appreciate walking in to the smell of fresh baked pie? Or would it make his day to return to find a home repair completed that has been put off for ages? What would make him feel appreciated?