I have clear, glass shower doors in our master bath. I'm not one that really cares that they sparkle 100% of the time. However, when I clean them, I want them shiny and clean with as little effort and scrubbing as possible. I live in an area where we have a lot of minerals in our water and when it gets on a solid surface and dries out, it definitely leaves deposits behind. I have used store-bought cleaners in the past where I have to scrub-and-scrub and can still feel soap scum and mineral buildup remaining. I now avoid the commercial cleaners and go for something much more simple that works.
Here are two thrifty cleaning methods for different styles of cleaning.
Weekly to Monthly Cleaning
For those that don't care if there's a little build-up from day-to-day but want to easily clean their glass shower doors, use vinegar and a sponge with a scrubby side to it. You can easily pour vinegar onto the sponge and scrub the shower doors with the rougher, scrubby side of the sponge. It takes very little elbow grease and will leave your doors sparkly clean when you're done. Sometimes I have to scrub areas of the doors twice because it's hard to see if there's any build-up left unless you squeegee them. I have found vinegar to be the best product to remove the mineral buildup left from our water. This also works well on my refrigerator water tray. I can scrub off a moderate amount of build-up in about 30 seconds to 1 minute fairly easily.
My sister also has glass shower doors and she prefers not to allow any build-up to occur because she doesn't like having to scrub the doors. Nearly every time when showering, she applies a light layer of conditioner to the glass and leaves it on while she takes her shower. At the end of the shower, she rinses the door off. Her glass doors are always sparkly clean and don't need to be cleaned at other times because this method leaves them constantly clean.
Both of these methods are very thrifty because you don't need to buy harsh chemical cleaners and can use what you already have. If you use expensive conditioner, you might consider picking up a bottle of inexpensive (or free with coupons) conditioner for cleaning if you like the second method of cleaning. Vinegar is always inexpensive and is great to purchase in large quantities.