What did they offer you such that "Work for free and bear all project risk" is an attractive option?
1) Charge for bespoke development as per usual.
2) Negotiate such that you own the IP after the project is over.
3) Use the IP to build the SaaS.
4) If they want to migrate to your SaaS and take advantage of ongoing improvements for your standard monthly rates, wonderful. If not, maintenance at your prevailing contract rates or via a negotiated maintenance contract.
1) Charge for bespoke development as per usual.
2) Negotiate such that you own the IP after the project is over.
3) Use the IP to build the SaaS.
4) If they want to migrate to your SaaS and take advantage of ongoing improvements for your standard monthly rates, wonderful. If not, maintenance at your prevailing contract rates or via a negotiated maintenance contract.