The MHRA Style Guide Online
A Handbook for Authors and Editors • Third Edition
From Chapter 8, 'Dates, Numbers, Currency, and Weights and Measures'
Words should be used to express simple sums of money occurring in normal prose:
The manuscript was sold for eight shillings in 1865.
The reprint costs twenty-five pounds or forty euros.
The fee was three hundred francs.
Names of foreign currencies, including the pre-2002 European currencies, should be given in their English form where one is in common use, e.g. ‘[Swedish] crown’, ‘mark’ or ‘deutschmark’ (not ‘deutsche Mark’). Note, too, the use of English plurals such as ‘drachmas’, ‘pfennigs’ (but ‘[Italian] lire’).
Sums of money which are awkward to express in words, or sums occurring in statistical tables, etc., may be written in figures. British currency before 1971 should be shown in the following form:
The manuscript was sold for £197 12s. 6d. in 1965.
UK decimal currency should be expressed in pounds and pence separated by a full stop on the line, not by a comma:
£12.65 (not £12,65 or £12.65p)
Sums below one pound should be shown thus (without a full stop after ‘p’):
The same conventions apply to sums expressed in euros, dollars, or yen:
€250, $500, $8.95, 25c, ¥2000
Where it is necessary to specify that reference is to the American, Canadian, or some other dollar, an appropriate abbreviation precedes the symbol without a full stop or a space:
US$, C$ (or Can$), A$ (or Aus$), NZ$
In most cases, abbreviations for (Swiss) francs, Scandinavian crowns, or pre-2002 European currencies follow the figure, from which they are separated by a space, and are not followed by a full stop, e.g. ‘95 F’, ‘250 Kr’ (BF, FF, SwF, DKr, NKr, SKr where it is necessary to specify Belgian, French, Swiss, Danish, Norwegian, or Swedish currency). However, the abbreviation ‘DM’ for the German mark precedes the figure and is separated from it by a space, e.g. ‘DM 8’.
The names of other currencies are best written out in full:
350 escudos, 500 pesetas, 20 roubles