Ashford do a fairly large Turkish Spindle at a reasonable price. You can get cheaper spindles at a few £s. If you have to buy it online, I would suggest the Ashford Turkish as you don't need to adjust it, whereas most ordinary top and bottom whorl spindles will need at least a small degree of adjustment. I have one and use it for spinning medium weight yarn, so it would suit a beginner (my OH can spin using it - I did also find him teaching someone on my wheel when I'd gone for a wander at the show today - it's amazing what he can do when I'm not looking
). You don't want too lightweight a spindle when you are starting out as it will not keep turning for long enough with thicker beginners yarn, nor do you want one which is too heavy as the yarn will keep breaking and you will get discouraged. Perhaps Sallyintnorth and Dans can describe their 'park and ride' method of spindling, which is great for when you first start out, and prevents a lot of frustration and confidence loss.
Muscles - wrists a bit, hands and fingers of course. If you are not sitting or standing comfortably you can get sore shoulders or back, as with a wheel. You also need to hold your arms up somewhat.
Carding can give you rsi in the wrists and the first joint in the thumb - if that can be a problem for you I will tell you how I deal with it - if only I had know 17 years ago I wouldn't have the problem now