There is probably already a budget to support you (Score 1)

Your manager probably has a defined training or employee development budget (that you may not know about). Ask directly if/what that budget is and how much of it can be used for professional development toward the costs of the conference you wish to attend. The other angle is to plan ahead and make it part of your goals during an annual review, write it out as a goal on your self evaluation when it's review time.