Cost of labour is the fulcrum, if you're capable of swinging a spanner and holding the right end of a soldering iron, the only labour cost with N/A-T will be for mapping, but if you're spannerlexic, labour expenses dictate that a T.T. conversion ends up costing less.
Here are rough figures for this equation demonstrating why 'shoestring' and 'spannerlexic' can't fit into the same sentence.
N/A-T 500bhp; has been built from as little as £500 and with a Hybrid transmission and mapping adding up to around £1k.
N/A-TT 325bhp; GTE lump £2-3k, manual trans £2-5k, labour £1-2k, or for 400bhp add another £1k for BPU, or up to 800bhp with a big single etc, for around another £10k.