When I started cooking sous vide I had difficulties to decide which vacuum machine to purchase. Finally I bought a non professional vacuum machine (Lava 100) which is powerfull and high quality made. This vacuum machine was a big investment (EUR 250) for my student budget.
When surfing on the excellent CookingIssues.wordpress.com site I found a very interesting post about vacuum machines affecting textures of ingredients (click on the image bellow for a direct link to the post).
To sum up this post I would say that there is no need of a powerful vacuum machine for vegetable, fish and poultry (such as chicken). CookingIssues even says that for some ingredients such as chicken, the more you increase the amount of vacuum the more you affect the texture and the flavour! On the other hand CookingIssues did not mention any drawback regarding high amount of vacuum for meat.
Just to say that sous vide cooking at home is definitely possible with a cheap vacuum machine. Remember that the issue consisting in sealing sous vide a marinate can be solved by freezing the marinate.