uuuusually to budget for a engine conversion you budget 2 to 3 times the cost of the engine to put it in.. but as this is a 26 replacing a 25 the engine part of the conversions shouldnt be too much or too hard, but all the supporting components will have to be brought up to spec, ie driveline, transmission, brakes etc..
for instance i got quoted $16,000 to put a s6 13btt in my mx5, the cost of the engine was $3,500.. and this was by the best workshop qualified to do this conversion.. the reason the price was soo much was because the only thing that was going to be mx5 at the end of the conversion was the shell..