Using old texts for ECE, TECEP and straighterline

[fretbrner]

Hello,

All of these have recommended texts and some still are a bit dear in price. Would getting an edition 1 or two before the recommended text editions be sufficient to use as the main text?

I realize that there are updates between revisions and editions, but are they really worth the extra $50 to $60 dollars if I wont be using them for as required texts for a full length course?

Thanks