Have you considered Athens? It's easy and cheap to get to, the entry fee is reasonable, the organisation is first class, you start in Marathon itself, it's in Autumn so you get to train over Summer, and best of all you finish in the Panathanaikon Stadium. It's not the easiest run though - a gradual uphill from 10 miles to 19 miles left me running on vapour for the last 10k.
I'm in but not through the ballot. I got a guaranteed place due to being unsuccessful in the last three ballots. Flights and hotels booked. Can't wait - just got to get through the VLM in a fortnight first!!
I don't have personal experience having never used a company, however speaking to a couple of Brits who ran Athens last November using one of the big firms, I wouldn't touch them with a barge-pole. They didn't receive the service that they thought they had paid for - no meet and greet at the airport, no-one at the hotel to talk through the schedule of events, and nobody to approach if anything went wrong. The premium they paid effectively gave them times and tickets for the connections between airport and hotel.
The ballot opens on 24th April, so I'm giving that a go. If successful in that, I'm sure I can sort out the rest myself.