First visit a dentist to diagnose the reason for those gap. Then the doctor can tell you all treatment options within your budget.
Next Steps
Your doctor will help you to decide that the Braces will be required/possible for correction of gap or not. Charges depends on braces type, treatment duration.
Health Tips
About " with braces it may have chances of teeth falling", any wrong treatment will give bad results. Proper diagnosis of your problem and treating as per standard protocol will give successful result. Don't worry. Visit a nearby dentist to clear all your doubts.