Craig's list, gumtree, preloved and eBay. I would go to your local dealer of any machines. They will have trade in when people are upgrading a machine.
A local dealer will service your machine if he is willing to do this you will have a good machine. Some dealers also sell ex demo models again only been on show or used at a class.
From what I can remember a larger throat usually means more money. The cheapest I can think of is a juki but the wide throat only goes backwards and forwards. No idea of cost in other countries.
My very first machine was a brother qe400 machine.
There are people on this site who use vintage machines with beautiful results look at vintage pages.
The throat sizes must say are expensive but quilt as you go isn't. It is only near the very end that have a large quilt to put together and all quilting is done before you join join sections.