Sage
Ah, this is obviously some strange usage of the word “affordable” that I wasn't previously aware of. (With apologies to Douglas Adams.)
No apologies to Douglas necessary (still a tragic loss though

), a fabulous use of an amazingly good original quote! (albeit "affordable" substituted for "safe"!) +rep for that alone! 👍
Affordable relative to what? I make ~$70 - 80K per year, therefore a $50K isn't affordable. However, to some folks $50K is a drop in the ocean and to them why would you buy an MX-5 when you can buy the extra status of the Boxster or an Elise?
But, to elaborate.... the MX-5 Miata is by far the most easily accessible roadster, to most people simply because it's the most modern longest running roadster on the market. I know there's still old roadsters out there like Spitfires and MG Midgets that can be had cheap, but with an all round driveability and safety taken into account, the Mazda is far and away the winner. Your average Joe can afford a MX-5 Miata, but even an S2000 or Z4 is almost twice the price, then you go up from there....
It depends what you need. The Mazda will quite easily break the speed limits of most countries in under 10s. Anything extra you spend means you can break the speed limits quicker, but you're paying lots of extra cash for power you can't use (unless you're lucky enough to own an airstrip or a racing circuit, or you live in Germany!) To my mind, owning a roadster is about being able to go out, drive a fun FR car, with the top down as much as possible.
From personal experience, anything over about 85-90mph with the top down, and no crash helmet becomes unpleasant.
I LOVE the S2000, in GT4, and would have loved one in real life, but there's no way I could have picked up one for the $7900 I spent on my MX-5.
The TVRs are absolutely

some but I can't buy one here, nor could I safely justify spending the asking price if they did.
The Solstice and Sky, are based on proven Elise/VX220 running gear (I think, although I'm probably wrong) but are priced for the US market, far lower than most of Europe and the rest of the world, and therefore are good value here.
But they're still playing catch-up as far as appeal goes to the Miata, which has over 15-years experience on them.
Condraz23
Personally, in terms of value-for-money, I would prefer the older 1989 Mazda MX-5. It looks good and has almost-perfect handling for an FR vehicle. They're only about $3,000.00 here too. Too bad it only has 128HP, that's less than an old Daewoo Lanos.
Actually the '89 Miatas only had the 118HP 1.6L engine. You have to look a few years down the line for the upgrade to the 1.8L engine with 128HP.
128HP is enough for some tail-hanging fun given the right roads and right conditions. Guaranteed, you're not going to win any 1/4 mile contests in a straight line in one, but who's interested in straight lines anyway?

Remember, power is nothing without control.
One notable OTHER, is the Toyota MR2 Spyder! What about that? A nice affordable little roadster.
Although in terms of practicality, it's 1.9 cu.ft cargo capacity is hardly a useful car! At least with the Miata, I can take me, the Missus, a tent, 2 sleeping bags, camping mattresses, a bag large enough to fit 2 changes of clothes, 2 cycle helmets and get 2 mountain bikes on the bike rack, and keep the top down, on a camping trip (usually with a winding wiggly road involved for good measure!)
Half the fun of a roadtrip is getting there, right?
