So difficult to give you advise without more info.
Package or DIY?
Airports?
Thomson holidays have a flight going out of Glasgow 13th August for 2 weeks, incl Maingate Lakeside, total cost £2870.00 using the £40 code on their site, less £15 Quidco = £2,855 Same holiday/hotel/dates(12th Aug) with VH would be £6449.60
Struggling from London,
2 weeks at a value resort from Glasgow £3,548 but from London £4,824.
Only cheaper flights I see are after 20th August, fly 21st August and return 4th Sept with Monarch for £545pp (didn't get exact price as its probably too late for you)
I think you will struggle so near, August is not a good month for late deals unless you are willing to fly from any UK airport, that will increase your chances.
We are doing 2 weeks at the end of Aug (19/08 to 03/09). We booked in April via the US Disney site when they had free dining (ended mid-May) but it did not start till 25/08 so we are staying offsite at the start (could have gone cheaper but decided to stay at Universal for the first 6 nights)
May not be the cheapest but for our family me, DH and DD & DS (14&12) :
Flights @ £489 each = £ 1956
9 nights Disney Caribbean Beach with 9 day park ticket hopper, full DDP = $3100
6 nights at Royal Pacifc Resort Universal = $1000
Universal tickets 4@ £90 = £360
Based on current 1.5 exchange rate cost is around £5000 for 4 of us (both kids are classed as adults here)
As I say - may not be the cheapest but it is realistic of cost without price glitches or a gazillion airmiles to bag cheaper flights - hope this helps