Take the plunge and spend a little more on the B4.1 in the first place!
It's as good a starter car as it is a full race spec car. It almost doesn't need any upgrades even to get it setup the same as the ones you'd see regularly running around the top finals at the nationals...but there are some things that help that you won't be able to resist if you stick with it and get the bug
Parts availability are second to none, and most people have run them at one time or another so setup advice is plentiful trackside as well.