Here are my favorite small garden books that have good ideas for the frugal gardener:
Square Foot Gardening by Mel Bartholomew---if you're only going to have one book on gardening, this is it, especially if you're a beginner.
The Postage Stamp Garden Book by Duane Newcomb---This book predated Bartholomew's book, but was less well-known. The original edition is probably hard to find, but I think they've published a newer edition.
How to Have a Green Thumb Without an Aching Back by Ruth Stout---I love this one, first published in about 1955. This one is fun to read (I want to be this kind of old woman), but the main thing to take from it for use in your garden is the use of deep mulch to make gardening as time-efficient as possible, and done right, it will build soil fertility over time.
How to Grow More Vegetables Than You Ever Thought Possible on Less Land than You Can Possibly Imagine by John Jeavons---There's a lot of activist stuff in this one, but you can breeze past that and get to the meat of the approach which focuses on getting the highest level of production out of the least space. It can be labor intensive getting started, but this is a great approach for someone with very little space. There are also some great tables. There are more recent editions, I think, including one that I believe includes Fruits in the title...
I'll write more about gardening for frugality on other days, but I did want to suggest that you focus on garden plants that get the most value for the space and work. Eggplant and tomatoes and peppers are fairly expensive at the store, but while they need between 12 and 18" of space each in a garden bed, 3 or 4 plants of each will produce as much as most people can eat and keep producing over a period of time if you pick the right varieties. Potatoes, while very productive, are cheap at the store and only worth growing if you have the space and time. You can grow a lot of carrots and onions in a small space, but they're cheap at the store and labor intensive to grow. Cucumbers and squash tend to be space hogs. Leaf lettuce and swiss chard can be a great choice because you can keep cutting a few leaves at a time for a long harvest. Herbs can be particularly good because they tend to be very expensive at the store, but most can be harvested continously over a long period (and some like rosemary are low maintenance perennials).