If the DJ's proposal is slightly above your budget, you may be able to negotiate.
Do not immediately decline the proposal. Instead, use the Messages tab to chat with the DJ. You can ask if they would be willing to adjust their rate, or perhaps offer a shorter set time to fit your budget. If the DJ agrees, they can edit the Proposal and send you an updated version with the new price.
Note: Not all DJs are open to negotiation. Check their profile to see if they have "Rates Negotiable" turned on.