List prices suggest that you'll be paying from around £55,000 for your Exige S in coupe form - with not much more for the open-topped Roadster version. About the same, in other words, as you'd have to find for a normally aspirated entry-level Lotus Evora coupe.
If, having considered all of this, you conclude that it is an Exige that you really want, then realistically, since very little equipment is included as standard, you'll need to set aside a £6,000-£7,000 budget for key extra options. Of these, the most crucial is the £2,000 'Race Pack' that as well as launch control and stiffer suspension adds the fourth 'Race' mode to the DPM Dynamic Performance Management System - a feature I can't imagine any self-respecting buyer of this car would want to be without. Apart from anything else, the lack of it is anyway going to make this Exige difficult to sell on.
By the same token, I can't really see the point of Lotus having gone to all the trouble it has in making this car so much easier for day-to-day use if prospective owners aren't going to properly trim the cabin to suit. That means putting aside up to £2,000 for one of the 'Premium Packs' that'll give you things like sound insulation, floor mats, a sports steering wheel and leather trim. Other essentials include air conditioning and rear parking sensors, while track fiends may like to specify the option stickier Trofeo tyres. Less important is the 'Convenience Pack' that adds things like cruise control, a USB connection and a cupholder.