colosfi - that really depends. There is not really one overarching book on Roman Provincials and most of them are not in English.
Probably the nearest thing is the set of Varbanov's four books - originally in Bulgarian but now also in English
http://www.varbanovbooks.com/Introduction.htmlbut even then that only covers the Balkan region and doesn't attempt to look at the hundreds of mints in what is now Turkey and the middle east.
And they are not cheap - probably about £250-£300 for the set.
Then for each other city or area that you look at you would probably have to look at a specialised reference - and again they are not cheap either. For example, the city of Deultum (also covered by Varbanov - but he doesn't illustrate everything) would be a volume of the Ruse collection as part of the Sylloge Nummorum Gracorum series. I think mine cost about £60 but it's by far the best.
The Sylloge Nummorum Gracorum is a set of books covering the Greek issues but which, in some cases, cover Roman Provincial issues as well. They are disparate, in French, German, Bulgarian, Italian and Spanish as well a a few in English. They used to be the only source of information on Roman Provincials but increasingly there are other sources available.
For Nicopolis ad Istrum and Markianopolis issues there are two excellent books from Hristova/Jekov. They are well illustrated but they are only available in Bulgarian.
Then there are the British Museum collections - the RPC (Roman Provincial coinage). They have only issued three volumes to date - but a fourth in conjunction with the Paris museum is due out -- but it's been due out for years - I've contributed some coins to it. They will probably set you back about £300 for the set.
If your interest lies in collecting the Provincial coinage of one particular child emperor like Diadumenian - then I'd really recomend this one
http://www.lulu.com/product/hardcov...nian/6318745It's really good and very reasonably priced -- but then I would say that as it's mine :)
I think if I were you I'd stick to online references for a while until you see how you get on. It would be easy to spend £2,000 on Provincial references and you still wouldn't cover everything.
This link is to the books I used when compiling my own material
http://www.diadumenian.com/references.htmlgood luck