It takes more creativity to make it memorable or romantic than it does money. It is a big day for the lady to be married though. I don't know how tight money is for you but, you only get married once (in theory at least) so to over extend just a little to make sure it is a wonderful day for her might be a good investment. She'll carry those memories for a long time.
Nevertheless, like I said, memories come from being romantic with it and that is more creativity than money. I learned that early on. I can see where it could be possible to do the wedding on a shoestring and make it very memorable for her, depending on her personality. She likes nature and hikes and so forth, that makes it easy in my mind. An outdoor wedding could be very very romantic. The Pastor would very probably be free for the ceremony.
I'm engaged also and our wedding will be on a shoestring. I am lucky, in Colorado, one is allowed to solemnize our own wedding, which is the way it should be anyway I think. Sure we have to buy a 30 dollar license, but then we can come home or wherever and pray to God to dedicate our marriage to Him. We will write our own vows to each other and will not even have a Pastor to officiate anything. The Lord has given us authority to ask and deal with Him directly. Our local laws allow for it also so it will be very private and small which is ok with both of us. But all of my fiances family lives overseas anyway and it is unlikely that any/many could come anyway. So a little creativity is in order to make sure that it will be romantic and memorable for her. I have some ideas I am tossing around but have not carved anything into stone yet. Luckily, my fiance is not materialistic in the least, and in fact suggested that we keep it small.
Like I said, I don't know your situation, nor your girls preferences, but it is possible, if perhaps she is of the right character to receive romanticism over materialism.