There are lots of decent sprayers around from 1.5 L upwards,
but you don't really need anything expensive , as long as it has a good brass nozzle.
I use a cheap Wickes 5L jobby, but with the lance cut off & a
short brass nozzle attachment fitted cut from a 1.5L sprayer.
Its a DIY job but works brill.
I don't like the small 1.5 L upholstery sprayers, if you have a large job you are forever stopping to re-fill. I always fill up at home with hot water, then it saves time on the job.