The big-box home improvement stores have service disconnect boxes and small load centers. They sometimes clearance them because sales are low. I bought my last 75 amp load center for around $25, IIRC.
An alternative is to buy surface mount breakers and wire up the distribution from those. You can make it all look good by mounting the breakers on a piece of aluminum plate. Here's a good place to shop for circuit protection:
Waytek Wire. Mounting three surface mount breakers will use about 1/8 -> 1/4 the space of a steel box. If you'll pay the price, the Cooper-Bussmann manual breakers are the way to go, they even sell a sealed Marine type (not necessary, IMO).
