I reckon for a decent engine, including wiring loom etc you are talking around £400 mark.
Then if someone was to fit, maybe a full days work - £150 maybe more. Then the disc conversion will cost a few bob and other bits. I reckon your probably looking at a rough estimate of £700 - £800. Then on top of all that, you need to tell insurance company, they charge for a conversion than a normal VTR.
Save up for a VTR, take mods with you. Best option...