Yes an 8 shaft is a good investment, many weavers do find they want more shafts than 4 after a while. However, you can pick up older style 4 shaft looms for not much at all, or buy a more modern one secondhand which you can then sell on, for much the same as you paid, if you do decide you want more shafts later.
Dryad, Harris and Weavemaster 4-shaft looms come up fairly frequently, often £50 - £100. May need a bit of TLC - new heddles, replace apron, etc - but often will work perfectly well. Great to get started on and decide where you want to go with your new craft - what width, how many shafts, portable or not, treadles or not, etc. Then you can pass along to the next beginner
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Ashford and Louet multishaft looms cost considerably more, but will hold their value, so again you can buy a 24” 4-shaft, use it for a while, then sell it on if you decide to buy something else.
Or, if you are like me, you find reasons to use all your looms, and the flock just keeps growing...
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However, if I ever come across a nice 16” Ashford 8-shaft I will happily buy it and sell the 4-shaft I learned on. The 16” is great for taking to Guild, workshops etc; the 24” I generally keep at home. One day I may buy a Louet David 90cm or even 110cm floor loom, but for now I am not considering anything wider than 24” (which gives 16 to 19” wide finished fabric.).
Personally I find table looms very uncomfortable on the table top, so I always get the stand. They are horrendously expensive, but to me a necessity. Lots of handy people make their own simple stands, however, and loads of people just use them on the table top.
Post an ISO on Ravelry UK Weavers, and the FB group(s), and you are very likely to turn up a few options.
Also, keep checking Loom Exchange for new ads - there are loads of ancient ads there, ignore them, but check daily for something you’d want and act quickly if you see one.