As reported by The Flight Deal, United Airlines has flights on sale from Boston, MA to Monterrey, Mexico for $166 round trip on select dates in April-May and August-September. While dates are limited, they are easily searchable via Google Flights:
Most United fare classes earn mileage based on distance if credited to Singapore Krisflyer, so this round trip flight may earn up to 4,000 redeemable miles with Singapore Krisflyer. We recently wrote about an opportunity to earn 500 free Krisflyer miles just for signing up for a new account.
While I don’t know much about Monterrey, I do know that Marriott, Hilton, and Starwood all have Category 1 hotels there:
At just 7500 Marriott points, 5,000 Hilton points, or 2,000 Starpoints for a weekend night (3k per weekday), the increased signup bonuses on all three cards would go a long way towards a cheap vacation! Check out each on our Best Offers page or see our write up on the Hilton offer, the Marriott offer, or the SPG offer.
You can read more about the airfare sale here or check the Google flights links above.
H/T: The Flight Deal