Yes my budget is a bit vague.
Its a budget that I set at the outset but I have been known in the past to go over my initial budget, sometimes way over. My overall budget for this year is around £2.0k which I plan to spend on a subwoofer, an AVR and with luck a pair of MA Silver FX surrounds but my goal is value for money. I'm not a big audiophile so optimum audio performance is not the goal. The aesthetics though are important even though the sub will be behind my sofa and not really seen, I like a nice looking sub.
Dual subs are unlikely to happen, not in this house anyway. I could squeeze in a couple of small sealed subs, XLS200 for instance, but for a pair of larger ported subs I don't have the space. I get what you are saying about the advantages of dual subs though.
The AVR purchase is another thing as at the moment new ones are over priced IMO and used ones are silly over priced IMO so I will likely have to wait until later this year. At least my existing Denon is working well and the next purchase will really only be for 4k support.