BWI-LAS is $300 roundtrip, if you spend 1 night in LAS (or take a red-eye back). Connect via LAX on the outbound and you should be able to get close to 5.5K.
IAD-SFO-MRY is doable as a same-day turn, for approx. $320 and gives 5.9K EQM with 500-minimums. Other airports in California where you connect via SFO work too, like RNO, BUR.
DCA-ORD-SJU is 5368 miles r/t for $350. Also doable as a same-day turn.
These are all available during the week of Dec 15.
These look good, but I am not getting the same prices. For example - how do you find the BWI-LAS at $300? I'd take that one, but the best I see is $390