How much?

Sosua to Santo Domingo is RD$240. Ride takes 4.25 to 4.50 hours, including rest/snack stop in Santiago.

Price of budget hotel depends on your definition budget. Where I stay costs RD$600/night for one bed, RD$750/night for 2 beds, but they may be more budget than you want.

I don't think you can compare Santo Domingo with the others on your list

Ken said:

Sosua to Santo Domingo is RD$240. Ride takes 4.25 to 4.50 hours, including rest/snack stop in Santiago.

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Ken, she asked for the price of a return ticket, which I believe is European for round trip. If that's the case, it would cost RD$480.

prices

you can find some decent (clean, secure, maybe pool) hotels near the colonial zone/gazcue for $30-40/us, which is budget. do a search here and you'll find several names like dona elvira, casona dorada, etc.
i actually quite liked the hotel delta on sarasota ave, but we're talking $60/night booked on their website + taxes.
as far as food, you can find the usual dominican-style places about the same prices as north coast and more ethnic (chinese, mexican) as well as fast food like pizza hut, taco bell, mcdonalds, etc. however, if you want a nice meal, be prepared to pay considerably more. i went with 2 friends to a steak house, similar to an outback restaurant in the states, paid $65 for 3 people - and that's not even a fancy place. a chinese place on sarasota was about $110 for 4.
i should add this was just dinner, no wine, no liquor.