I agree entirely with Steve.
17k is a lot for a conversion.
Of course, it depends on your specification, although some convertors adopt the attitude of 'this is what we do. take it or leave it".
One thing to consider is the compromise between an experienced convertor with a significant financial turnover and therefore legally compelled to charge you VAT; hence, effectively a 20 percent surcharge, or a qualified carpenter / electrician that will not be obliged to levy VAT.
The latter may not have the experience, and competence you will need !
I located such a rare, talented craftsman, who, unfortunately no longer undertakes conversions.
I could provide you with the details, privately, on the understanding that he will almost certainly decline your business.
Were he to agree to undertake your work I expect you would save 50 percent of a 17k budget.
A key decision is pop top or not; as they are expensive. My guess would be 5k minimum !