We've always struggled to find accomodation between Christchurch and Picton when we're crossing between islands on the ferry (a regular occurrence, sometimes once or twice a month).

We've narrowed it down to two options:

1. Stay in Kaikoura on your way south after crossing from Wellington to Picton.
2. Stay in Blenheim on your way north, when you're about to cross from Wellington to Picton.

In Blenhiem (and Kaikoura) we've bounced around various motel and hotel options before settling on our favourites.

For Blenheim, it's the Chateau Marlborough hands-down. It's got a proper 24/7 reception, generous carparking (wide enough for our Porsche Panamera and Volvo SUVs), there's a nearby supermarket for snacks/self-catering, and good cafe/brunch options nearby.

Rooms are clean, tidy, modern. Never had a bad stay. Despite being billed as "luxury" we've found the price to be very affordable and similar in price to motel accomodation.