I think if you plan carefully, can stay in an occasional studio and don't need to stay in Gold Crown Resorts, you should no trouble getting 8 weeks from 110,000 points, especially if you watch for sales where the number of points required are reduced. We have 77,000 RCI points and always have no trouble getting between 3 & 5 weeks by staying in 1 bedroom units and travelling in shoulder or off season (ie; FL in the fall). When searching on RCI, I always look in the "7 Night Exchanges under 10,000 Points" section first. Most of the units there are studios but I have seen 1 and occasionally a 2 bedroom unit. Those can be booked many months in advance unlike the exchange vacation deals which are usually a shorter time frame. As mentioned above every exchange has a fee so that cost adds up where as when you use all your points for 1 stay you would only have 1 exchange fee.
When looking at resorts in Cancun read the fees section carefully. Many resorts are mandatory All Inclusive and those fees can be well over $100. per person per day which when combined with your exchange fee and the use of your points can end up being a very expensive week. You will also need to factor in airfare and transportation to/from the airport. We are Canadian and have found with our expensive airfares (we, personally, don't have any frequent flyer programs) we can book an AI vacation, including airfare and airport shuttles, for almost half of the cost of just the AI fee when booking through RCI. YMMV.
~Diane