Viking River Cruises (www.vikingrivercruises.,com) is one of the largest river cruise companies in the world, with many interesting itineraries. Until recently, a few of their cruises, such as the one of Ukraine's Dnieper River and the Balck Sea, were also reasonably priced.
Unfortunately, that is no longer the case. The Ukraine cruise, for which I paid about $2100 in 2010 for a single cabin, is now quoted as starting at $4638 per person. The current price is for 12 days, whereas the earlier cruise lasted 11 days. There may be reductions from the quoted price for early booking, repeat passengers, and so forth, but clearly this cruise has moved out of budget range.
The Dnieper cruise is a great way to explore this fascinating and, at least to North Americans, little known part of the world. If you want to read more about it, refer to blog posts for the latter part of 2010. It was probably the most interesting cruise I have ever taken, out of a dozen or so. And it provides an easy way to see many of Ukraine's top attractions, even if you don't speak Russian.
Below is a picture of a statue in Kiev of one of the Cossack hetmen who ruled Ukraine in the old days.