I think we are talking PHRF here so no nationals and I may have heard the word affordable used as well while I'd definately ask the national champions what they are buying, I'd use that as the "what not to buy option". In terms of getting these most most for your buck, the approach I've taken is as follows:
1) make sure you have a good / great head sail for your dominatant STARTING conditions. Upwind speed is most important at the start so you best bang for the buck is the speed you need to get clear off the line. Aim for something that gives your "very good" over 2 - 3 years vs the material that fastet but needs replacing after a hard season.
2) Not sure what your sailing in / on but don't be afraid to consider dacron on the mainsail. Durability is a huge factor here - you can spend more but getting longiviity from this sail will free up loads of budget over a 3 - 5 year period.
3) Keep your kites fresh. You may cycle through a couple head sails during a race but your principal kite tends to be the same across a pretty good range and they matter more than most people realize. Again, fine tune this toward your dominant sailing condition.
4) Another factor is your boat, what conditions your racing in and who your looking to beat / what performance gaps your looking to fill. You may want speciality reaching, light air or running sails. Its possible to get a back advantage by having just the right package for specific conditions. Think carefully about your racing plans / conditions / competition and find an edge.
5) Ive listed it last but its really #1 - find a sail maker who has a fast product...competitive with the top lofts...and who you can trust to help you make the tradeoffs. You'll know you have the right dude when he tries to talk uyou out of spending money and asks lots of questions about the bigger pciture, whats the longer term budget, etc and is willing to recommend investments in items other than sails to improve performance. Talk openly and listen carefully.