If you're ok with DIY then Novakon has a "deal" going on now.
They have their NM-145 on clearance for $3950, 14x8x12" travels.
But you would get a mostly put together cnc machine with a few bugs to work out.
NM-145 | Novakon
I have no experience with Novakon and I'm not recommending them - just pointing out another option.
****I just reread your post about wanting 18" x travel so this fails on that point but has the higher speed you were looking for****