Pattern designs are primarily to keep lines clean. Design strength (this goes with any model) can be achieved by using heavier materials (which add weight and defeat the purpose) or by using light and expensive materials like carbon fibre etc (which lessen the weight of your wallet).

Either way, the newer pattern planes (of all descriptions and sizes) are designed to be handled with some care while gound handling. For example, I never taxi my pattern planes out, I walk them to the flight line, and I never taxi the plane back; once it has landed, I go and pick it up. These tactics increase the planes lifespan; I fly from grass. That leaves taking care of retracts following a hard landing; I usually upgrade the retracts (if the model uses them) with titanium struts (but then you are adding to cost).

An alternative, is to buy a sport pattern plane which is middle of the road compromise, can do sport aerobatics, some 3-D and some pattern flying. These models are usually inexpensive, comparitively speaking.

One of the lightest models is one from Hobbynet, Freedom or something similar; I think it comes under 6lbs, but it is fragile.
Fragile only if you are rough with it. There is a price advantage though, it is on sale for only $149.

There is a great 90/120/140 sized arf pattern kit coming out of my LHS very soon and it will be on sale for an incredible price.

Vim