Cheap seats will mostly be uncomfortable and/or will degrade in quality very quickly e.g a friend bought some drift brand seats and within 2 months the padding went to shit and felt like you were sitting on a steel park bench.

If you need it for just holding you in around corners then as long as it's a bucket it will do the job. You want comfort and something that will hold you tight then be prepared to pay.

However there is a sweet spot and I believe these seats hit them perfectly (Bonus points because they are ADR approved)
http://www.option1garage.com.au/Accessories.htm