There is no need for this hobby to be expensive as there are some shortcuts to help someone starting out. For example, it is not necessary to own a flower garden in order to take up the craft of flower pressing. If you live in a flat or apartment and still want to grow your own flowers you can grow them in containers on a patio or windowsill. In fact window boxes can be utilized to good effect being both space saving and aesthetically pleasing. It's really a matter of trial and error to discover what plants to use but generally speaking it is best to keep away from plants that have fleshy stems as these contain water.
Some colors last better, yellow in particular, whereas blues and pinks can fade over time.
By experimenting you'll soon learn which flowers to use and which plant matter will turn brown during the pressing process. For this reason don't use very bulky material. With larger flowers such as hydrangeas and delphiniums, remove each floret and press these individually. You will then end up with a larger stock of blooms to use in your work. Also don't forget the weeds growing on roadsides and in fields.