If they can double that kind of salary that easily there's something off. Assuming you're not the world's worst negotiator, why couldn't they afford to pay you more before? $100k is a lot of money. Doubling that without so much as a thought seems pretty frivolous to me but it doesn't necessarily mean they suddenly value your work more.
If you take their offer in the best case the deal will amount to golden handcuffs. Worst case, they'll try to extract all the domain-specific knowledge you have and you'll be let go on the next possible occasion.
Assuming your prospective consulting / contracting deals are more or less certain then you have a fairly safe platform to start a consulting business from. You'll have revenue right from the start, distributed among 2 clients, which significantly reduces your risk. Most importantly, with 2 clients lining up you already have the promising foundations for a potentially prosperous network, which arguably is worth a lot more than the money alone.
If you deliver high quality results and continue to expand your network and market your business $150k certainly isn't the ceiling for what you can achieve with a consulting business (while $200k in your current job might be).
Finally, depending on your location and on how close-knit your particular industry is burning bridges with those 2 clients might very well mean you'll have a much harder time starting your own consulting business later on.
Oh, and doing something for the money alone, particularly something shady like accepting and then moving on after 3 months anyway, is never a good idea.