Hi Smurfgirl,
Congratulations on your wedding. I have been to the Dominican Republic and Mexico (and Barbados, Antigua and the Bahamas). I wouldn't rush back to the DR but Mexico was fabulous. We stayed in Playacar which is a little way out of Cancun which I imagine would be more touristy and possibly tacky. There is plenty to see outside the hotels if you enjoy history. We hired a car and visited a couple of Mayan ruins sites and there are a couple of Eco parks in the area too.
I think the DR and Mexico are cheaper because of the volume of hotels in comparison with other Caribbean destinations. Also all the package tour operators offer charter flight deals to Mexico and the DR (and Cuba and Jamaica) whereas the smaller islands like Tobago, Aruba, St Kitts, Turks and Caicos and so on are more generally offered on a scheduled flight basis with Virgin, BA etc and this increases the cost.
The Maldives is generally considered one of the top honeymoon destinations because the islands are not promoted as family destinations and the hotels are small and secluded (one per island sometimes).
Dh and I got married in Mauritius which is also a beautiful and romantic island.
I think one of the main things you should consider is the weather which varies vastly from one island to another in the Caribbean. October can be the end of the rainy season and some islands are 'safer bets' weather wise than others in October. We were in the Bahamas for October half term last year and it was quite cloudy, wet and windy on several days.
Dubai is a pretty safe bet in October as far as sunshine is concerned. There are plenty of luxury hotels (check out the Al Qasr it's amazing) but of course it's not the Caribbean!
Generally the Sandals resorts are recommended for romantic couples' holidays - no children allowed. However they are usually much more expensive than other 5* All Inclusive hotels in the same destinations so IMHO I would save a little money and select another luxury hotel. I'd also skip Barbados for the same reason - it seems to be one of the more expensive Caribbean destinations from the UK. Antigua was nicer IMO. St Lucia is quite stunning because it is very green (it gets quite a lot of rainfall) and mountainous but, as the island is volcanic, the beaches do not have the pure white sand one might expect in the Caribbean.
I would also consider Sri Lanka and Malaysia - I believe that for an exotic destination they represent good value for money.
Bear in mind that wherever you decide to go prices will be much higher at the end of October which is half term.
Happy planning and do check out hotel reviews for ALL destinations on Tripadvisor . You can find out much more about the different Caribbean islands on the Caribbean-on-line discussion forums .