Yes, the six conversion is pricey, but if done correctly you will never regret it!
Six's get a bad rap from; guys that have never drove one, guys that will never spend the $ to convert one, worn out carbs, cobbled together conversion parts that don't work like they should, rusted over priced cars (I guess that applies to all vintage cars).
Personally I prefer a stock Motronic injected 3.2 or one of the small displacement MFI engines like a 2.2S. This gives you the "turn the key and rock" performance that is hard to beat. The 3.2's are less complicated to convert to 914 (compared to a later 3.6 engine), and the 2.2's have the best output to weight ratio of almost any of the Porsche flat sixes.
Do not do a six conversion with the hopes of recouping any of the expense. Yes, the car will be worth more with a quality conversion, but only do it because it is what you want and intend to keep for long term use. Key word being USE, as Porsches are best when used on a regular basis, driven in a manner that suggests you have stolen the car