Many used DJ controllers (especially Numark and Hercules) come with a full Virtual DJ Pro license or a transferable LE key. Check eBay, Reverb, or local marketplaces. Often, you can get the hardware + legal license for under $50.
If you have years of cue points, loops, and playlists in Virtual DJ LE 7.0.3, you can export them: virtual dj le 7.0.3 serial number
Serato Lite is the modern equivalent of "LE" versions. Free to download, limited to two decks and basic effects, but fully compatible with most entry-level controllers. No serial number required—just sign up for an account. Many used DJ controllers (especially Numark and Hercules)